He _____ football regularly for many years when he was young.

A．was playing

B．has played

C．played

D．had played

根据空调冷源的( )，可以将空调分为压缩式制冷机和吸收式制冷机。

A．工作原理
B．冷源设备布置的情况
C．制冷性能
D．适应情况