小明在探究平面镜成像的特点时，用一块透明的玻璃板代替平面镜的目的是______．实验时，将棋子放在玻璃板前，眼睛应该在玻璃板______（前/后）观察．小明将棋子逐渐远离玻璃板时，棋子所成像的大小______（变大\变小\不变）．

--- I        to your birthday party last Sunday.

--- Unfortunately, you were out on business.

A．had come

B．came

C．would come

D．would have come