China's icebreaker Xuelong  ______  by heavy floes since Friday after rescuing passengers on a Russian vessel stranded in Antarctica.

A．has been trapped

B．had been trapped

C．has trapped

D．was trapped

在（）过程中，外界加给系统的热量一部分用于增加系统的内能，其余部分用于系统对外界做膨胀功。

A.定压

B.定容

C.定温

D.绝热