— I’m afraid I can only make a small contribution this time.

—____.We really appreciate your assistance.

A．The best things come in small packages

B．The more,the better

C．It is better to give than to receive

D．Every little helps

电力系统中供测量和保护用的重要设备为（）。

A．变压器

B．互感器

C．调压器

D．箱式变电站