A.波源的波长发生了改变
B.波源的频率发生了改变
C.观察者收到的波的频率发生了改变
D.波速发生了改变
答案:C
You have done a good job in the competition. But you’d better ____your body language next time.
A.to pay little attention to
B.pay many attentions to
C.to pay few attention to
D.pay more attention to
电容式微量水分析仪响应极慢,可能的原因有()。
A、探头污染
B、探头开路
C、探头短路
D、样品流速过慢