工程材料在使用条件下所表现的性能称之为使用性能，它包括( )、化学性能及机械性能。

A．物理性能

B．铸造性能

C．压力加工性能

D．焊接性能

—What’s wrong with him?

—The picture he came across        his memory of a sad story in his childhood.

A．put off

B．took off

C．set off.

D．gave off