Her uncle likes playing basketball, he often      it on Sundays, but now he        .

A．plays, is fishing

B．is playing, fishing

C．play, is fishing

D．playing, fishing

一个篮球从空中自由下落到地面的过程中，它的动能不断________，势能不断________，机械能的总量__________（选填“增加”、“减少”或“不变”），此过程中机械能_________（选填“守恒”、或“不守恒”）。