The old man was taking a walk, ________ by his grandson. [ ]

A. supporting  

B. supported

C. being supported  

D. having supported

为了保证汽车能稳定的直线行驶和转向轻便，转向后能自动回正并减少汽车行驶中轮胎和转向机构的磨损，必须设置（）。

A.前轮前束

B.前轮定位

C.车轮外倾

D.主销内倾