问题
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．mark
B．chance
C．signal
D．measure
答案
答案：C
词义辨析。mark 标志，符号；chance 机会，运气；signal 信号，暗号；measure测量；尺寸。句意：在我们班的，当铃声响时，老师合上他的书，这对于每个人来说是一个起立的信号。故选C。