In our class when the bell rang and the teacher closed his book it was a for everyone t

问题补充：

In our class, when the bell rang and the teacher closed his book, it was a for everyone to stand up.

A. signal

B. chance

C. mark

D. measure

答案：

(答案→)A. signal

B. chance

C. mark

D. measure

解析：根据句意可知打铃及老师合上书本，这是下课的暗示，选项中只能选择signal。chance“机会”，mark“分数，痕迹”，measure“方法，措施”。