诊断子宫性闭经的依据是A．注射黄体酮有撤退性出血 B．注射黄体酮无撤退性出血 C．雌

As is known to all, _______ strong and powerful China will certainly benefit _____ whole world.

A．a; a

B．the; a

C．the; the

D．a; the

急性肾衰病人少尿期应限制()

A．碳水化物

B．蛋白质

C．水

D．氯化钾

E．葡萄糖酸钙

—Mary told me she would      computer studies.

—Really? I’ll try my best to ask her to     such foolish ideas.

A．pick up; give up

B．put away; give up

C．give up; put away

D．give up; pick up

造成野生动植物濒危和灭绝的主要原因是（）

A.自然选择

B.物种退化

C.人类对野生动植物资源的开发和利用

D.人类对野生动植物资源的过度狩猎或采伐，对栖息地环境的污染和改变

何谓急性阈剂量、慢性阈剂量？