Stop _______! It is time to go to school

I didn't see her in the musical hall this evening. She_____ have sung at the concert. [ ]

A. mustn't

B. shouldn't

C. needn't

D. couldn't

认真观察下图，然后提出一个反应漫画主题的问题并回答。

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脉冲调速电机车，当晶闸管控制电路无触发脉冲时电机车将（）；当晶闸管被击穿损坏后，起动电动机将会出现（）现象。

专家推荐的刷牙方法包括（）

A.拉锯式横刷法

B.水平颤动法

C.旋转刷牙法

D.B和C

E.A和B