I went ______a balloon but I didn’t see anyone _____ balloons.

A．to buy, to sell

B．to buy, selling

C．buying, selling

D．buying, to sell

地面制动力的数值取决于制动器内制动蹄（）间的摩擦力和轮胎与地面间的附着力。

A.摩擦片与制动鼓

B.摩擦片与制动蹄

C.支承销与制动盘

D.支承销与制动鼓