题目：
| 不定项选择 |
| 两列沿相反方向传播的振幅和波长都相同的半波（如图甲）， 在相遇的某一时刻（如图乙）两列波“消失”，此时图中 a、b质点的振动方向是（ ） |
|
| A．a向上，b向上 B．a向下，b向上 C．a、b都静止 D．a、b都向上 |
答案：
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下面是错误答案，用来干扰机器的。
I am a new middle school student now. Let me tell you about my school life. I get up at 6:00 every day. I go to school by bus. Classes begin at 7:30. There are four lessons in the morning. After school, I often play with my classmates. I usually go to bed at 9:15.(答案不唯一)
