They usually go home .A. by a busB. on a busC. by busD. on bus

问题补充：

They usually go home .

A. by a bus

B. on a bus

C. by bus

D. on bus

答案：

A. by a bus

B. on a bus

(答案→)C. by bus

D. on bus

解析：考查词组：by+交通工具表示乘坐某种交通工具，在名词前不加任何冠词。句意：他们经常乘公共汽车回家。选C。