A.human cloning will not succeed unless the technique is more efficient
B.scientists are optimistic about cloning technique
C.many people are against the idea of human cloning
D.cloned animals are more favored by owners even if they are weaker
A.rich people are more interested in cloning humans than animals
B.cloning of animal pets is becoming a prosperous industry
C.there is no distinction between a cloned and a natural dog
D.Missy's master pays a lot in a hope to revive the dog
开始考试点击查看答案A.lab technicians may be affected by chemicals
B.cats and dogs in the lab may die of diseases
C.experiments may waste lots of lives
D.cloned animals could outlive the natural ones
开始考试点击查看答案A.there isn't enough fund to support the research
B.cloning dogs is more complicated than cloning cats and bulls
C.Mr. Westhusin is too busy taking care of the business
D.the owner is asking for an exact copy of his pet
开始考试点击查看答案A.Animal cloning is a stupid attempt.
B.Human cloning is not yet close to getting it worked out.
C.Cloning is too inefficient and should be stoppe
D.D.Animals cloning yes, and human cloning at least not now.
开始考试点击查看答案A.traditional cultural heritage is worthy of preservation
B.the universal features shared by all cultures aren't worthy of notice
C.musicians pay more attention to the preservation of traditional music
D.the more developed a culture, the more valuable the music it has fostered
开始考试点击查看答案A.The lowest stratum is the understory, composed of palms, herbaceous plants (such as wild ginger), and tree seedlings and saplings. (41) . Many have deep red coloring on the underside of their leaves to capture some of the scarce light that does manage to reach the forest understory. This red coloring enables understory plants to absorb light of different wavelengths than do the plants with rich, green-foliaged canopy, the umbrella-shaped upper structure of trees. Above the forest floor but below the canopy are one or more midstory strata, made up of woody plants, such as large shrubs and midsized trees.The overstory is the canopy, in which the tree crowns form a continuous layer that captures the major part of the rainwater and sunlight hitting the forest. The height of the canopy varies from region to region and forest to forest, ranging from 20 to 50 m (65 to 165 ft). (42) . Researchers use hot air balloons, cables, catwalks, towers, sophisticated tree-climbing gear, and even robots to study the millions of plants and animals that make their home high up in the forest canopy. Canopy researchers also use huge cranes that are dropped into the heart of the forest by helicopters. Suspended from the crane's long, movable arm is a large cabin that functions as a mobile treetop laboratory. Moving from tree to tree, forest researchers collect specimens, conduct experiments, and observe life in the canopy frontier.The highest stratum of the rain forest is made up of the emergent trees, those individuals that stick up above the forest canopy. Emergents, which do not form a continuous layer, are usually the giants of the forest, reaching heights of 35 to 70 m (115 to 230 ft) or more, and trunk sizes of over 2 m (6.6 ft) in diameter. (43) . However, these trees tend to be so large that they collectively account for the vast majority of the woody mass, or biomass, of the forest.The nicely ordered strata of the rain forest, including the continuous layer of the canopy, are regularly disturbed by naturally occurring events, such as falling trees. Trees in a rain forest canopy are often interconnected by vines, and a falling tree may pull as well as push other trees down with it, producing a domino effect of falling trees. The resulting opening in the forest canopy enables light to pour onto the forest floor. (44) .Other natural disturbances create even larger openings in the forest canopies. For example, along the hurricane belt in the Caribbean and the typhoon belt along the western Pacific, some forests are substantially altered when high winds and storms blow down hundreds of trees every few decades. (45) . Scientists have found that these natural disturbances and the subsequent forest regeneration are a vital process that leads to healthy and diverse forests.A.New plants and animals then move into the area and begin to grow.
B.Just 2 percent of the sunlight goes through the many layers of leaves and branches above, so understory plant species have developed special traits to cope with low light levels.
C.On a smaller scale, large mammals, such as elephants, regularly destroy rain forest vegetation in the Congo River Basin in Africa.
D.An understory of shorter trees and a lacework of woody vines, or lianas, produce a forest of such complex internal architecture that many animals, including some sizable ones, rarely or never descend to the ground.
E.Less than one percent of the trees in the forest reside in the canopy and emergent layers.
G.Because more light penetrates the canopy, however, the vegetation of the understory and forest floor is better developed than in the tropics.
H.a. The lowest stratum is the understory, composed of palms, herbaceous plants (such as wild ginger), and tree seedlings and saplings. (41) . Many have deep red coloring on the underside of their leaves to capture some of the scarce light that does manage to reach the forest understory. This red coloring enables understory plants to absorb light of different wavelengths than do the plants with rich, green-foliaged canopy, the umbrella-shaped upper structure of trees. Above the forest floor but below the canopy are one or more midstory strata, made up of woody plants, such as large shrubs and midsized trees.The overstory is the canopy, in which the tree crowns form a continuous layer that captures the major part of the rainwater and sunlight hitting the forest. The height of the canopy varies from region to region and forest to forest, ranging from 20 to 50 m (65 to 165 ft). (42) . Researchers use hot air balloons, cables, catwalks, towers, sophisticated tree-climbing gear, and even robots to study the millions of plants and animals that make their home high up in the forest canopy. Canopy researchers also use huge cranes that are dropped into the heart of the forest by helicopters. Suspended from the crane's long, movable arm is a large cabin that functions as a mobile treetop laboratory. Moving from tree to tree, forest researchers collect specimens, conduct experiments, and observe life in the canopy frontier.The highest stratum of the rain forest is made up of the emergent trees, those individuals that stick up above the forest canopy. Emergents, which do not form a continuous layer, are usually the giants of the forest, reaching heights of 35 to 70 m (115 to 230 ft) or more, and trunk sizes of over 2 m (6.6 ft) in diameter. (43) . However, these trees tend to be so large that they collectively account for the vast majority of the woody mass, or biomass, of the forest.The nicely ordered strata of the rain forest, including the continuous layer of the canopy, are regularly disturbed by naturally occurring events, such as falling trees. Trees in a rain forest canopy are often interconnected by vines, and a falling tree may pull as well as push other trees down with it, producing a domino effect of falling trees. The resulting opening in the forest canopy enables light to pour onto the forest floor. (44) .Other natural disturbances create even larger openings in the forest canopies. For example, along the hurricane belt in the Caribbean and the typhoon belt along the western Pacific, some forests are substantially altered when high winds and storms blow down hundreds of trees every few decades. (45) . Scientists have found that these natural disturbances and the subsequent forest regeneration are a vital process that leads to healthy and diverse forests.A.New plants and animals then move into the area and begin to grow.B.Just 2 percent of the sunlight goes through the many layers of leaves and branches above, so understory plant species have developed special traits to cope with low light levels.C.On a smaller scale, large mammals, such as elephants, regularly destroy rain forest vegetation in the Congo River Basin in Africa.D.An understory of shorter trees and a lacework of woody vines, or lianas, produce a forest of such complex internal architecture that many animals, including some sizable ones, rarely or never descend to the ground.E.Less than one percent of the trees in the forest reside in the canopy and emergent layers.F.Because more light penetrates the canopy, however, the vegetation of the understory and forest floor is better developed than in the tropics.G.The rich, green canopy is teeming with life, and forest researchers have developed ingenious methods for accessing this mysterious ecosystem.A. B. C. D. E. F. G.
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