问题
选择题
5. In our class, when the bell rang and the taacher closed his book, it was a or everyone to stand up.
A．signal
B．chance
C．mark
D．measure
答案
A
signal 信号； chance 机会； mark 记号；measure 措施。句中的it 代替“铃响时教师合上书”这件事，而“它”正是大家要起立的“信号”。