相对剂量反应试验可反映机体（）的营养水平。
A.维生素A
B.蛋白质
C.维生素C
D.钙
参考答案：A
心脏停搏时间是指从循环停止到（）。
A.意识恢复
B.自主呼吸恢复
C.心脏自动节律恢复
D.重建有效人工循环
E.呼吸心跳恢复正常
He tried to deal with the increasing burden of his work,but he finally _____and had to take a complete
rest. [ ]
A. broke off
B. broke away
C. broke out
D. broke down
