问题
单项选择题
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
参考答案：A
解析：
根据句意可知打铃及老师合上书本，是下课的暗示，选项中只能选择signal。chance意为“机会”；mark意为“分数，痕迹”；measure意为“方法，措施”。故选A。