By the time she ________ home, her parents will have prepared some delicious food for her. 

A．gets

B．will have got

C．is getting

D．will get

下列说法中正确的是   [ ]

A． 晶体熔化时. 吸收热量，但温度不变    

B． 做功和热传递在改变物体内能上是等效的    

C． 分子之间只存在引力作用

D． 四冲程内燃机的做功冲程将内能转化为机械能