—Tom has been fired by his boss.

—________？As far as I know，he is a hard­working and considerate fellow.

A．Why not　

B．How come

C．What then　

D．So what

下列实例中属于机械能转化为内能的是 [ ]

A．内燃机的活塞在燃气推动下运动

B．点燃的火箭飞向太空

C．夏天，广场上的石凳被晒得发烫

D．陨石坠入地球大气层成为流星