题目

如图4所示，一列简谐波此时刻波动只发生在A、B之间，已知P质点正在向下运动，周期为T，则下述正确的是（       ）A．振源可能是N，波向左传播B．振源可能是M，波向右传播C．若N是波源，它已停振半个周期，但波仍向左传D．从振源起振开始计时，Q质点已振动半个周期   答案：AC解析: 从方框中选择适当的句子补全对话，有两项多余。A: Good morning.B: 1.A: Do you have a friend here?B: Yes, I do.A: 2.B: Oh. She is my friend, Amy.A: 3.B: She comes from the USA.A: She looks like Judy.B: 4.A: Are they in the same grade?B: Yes. 5.A: Is Judy your friend, too?B: No, she isn’t.A. Who is that girl?B. But they’re in different classes.C. Where is she?D. They are sisters.E. Good morning.F. Thank you.G. Where does she come from?