题目

The number of people invited to the party ______ fifty, but a number of them ______ absent for different reasons.    A. were; was    B. was; was   C. was; were  D. were; were 答案：C利用平面镜可以（    ）A．成缩小的像     B．改变光的传播方向   C．成倒立的虚像   D．成正立的实像