Bob said he was going to join our club but he didn’t. What a shame! He ______ his mind.

A．can’t have changed

B．mustn’t have changed

C．wouldn’t have changed

D．shouldn’t have changed

外界无火焰，油品在空气中开始自行燃烧的最低温度，称为该油品的（）。

A、自燃点

B、熔点

C、燃点

D、闪点