求原因.w,x,y,z,是原子序数依次增大的同一短周期元素,w、x是金属元素,y、z是相邻的非金属元

According to the passage, what problem does the recent research find？

A．Sleep shortage has become a worldwide problem.

B．Developed nations don"t pay enough attention to sleep.

C．Sleep problems are more serious in developing countries.

D．Lack of sleep is more obvious in developed countries.

请帮忙给出正确答案和分析，谢谢！

American students usually get their high school diploma at the age of______.

A．12

B．17

C．20

D．24

请帮忙给出正确答案和分析，谢谢！

What responsibilities do states have concerning education？

A．They must decide what certificate teachers should have.

B．They must pick out the suitable textbooks for students.

C．They must make sure every child can receive education.

D．They must provide enough funds for their schools.

请帮忙给出正确答案和分析，谢谢！

氰化氢中毒的毒作用特点是

A、与血液中Hb结合，影响氧的运输

B、血液中Hb虽被氧饱和，但不能被组织利用

C、抑制体内多种酶的活性

D、抑制胆碱酯酶的活性

E、降低脑和肝中ATP酶的活性，使细胞缺氧

请帮忙给出正确答案和分析，谢谢！

According to Kevin, most passengers______.

A．don"t refuse to talk with the taxi driver

B．keep silent when they take me ride

C．tell me driver how to go to me destination

D．don"t make any choice as to how to go to me destination

请帮忙给出正确答案和分析，谢谢！