采样定理要求采样采样频率至少大于信号频谱中最高频率成分fC.的（）以上，就可以不丢失原信号中所含的信息。
A.1
B.2
C.3
D.4
参考答案：B
The little boy ________ for the apples on the tree, but of course he was not tall enough. [ ]
A. handed out
B. went out
C. reached out
D. brought out
搬运昏迷伤员时应（）。
A.使用硬板担架
B.将伤员侧卧
C.让伤员平卧并抬高下肢30-50cm
D.抬高上身便于呼吸
