规定的观察期内某病患者中因该病而死亡的频率是
A.发病率
B.患病率
C.某病病死率
D.某病死亡率
E.治愈率
请帮忙给出正确答案和分析，谢谢！
The research carried out in eight countries______.
A．reveals the relationship between sleep problems and age
B．provides evidence that lack of sleep affects people"s health
C．puts forward the theory that sleep problems are a kind of disease
D．proves that sleep problems will lead to smoking and poor diet
请帮忙给出正确答案和分析，谢谢！
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！
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