The nurse is giving instructions to a client who is going home with a cast on his leg. Which point is most critical

A. Using crutches properly.
B. Exercising joints above and below the cast, as ordered.
C. Avoiding walking on a leg cast without the physician’s permission.
D. Reporting signs of impaired circulation.

下列说法正确的是（　　）

A．任何状态下处于任何位置的物体都具有内能

B．机械能大的物体内能一定大

C．静止在地面上的物体无内能

D．空中飞行的子弹比地面上静止的子弹内能多