Carl is studying        food science at college and hopes to open up       meat processing factory of his own one day.

A．/ ; a

B．/ ；the

C．the; a

D．the; the

冶金起重机的车轮．联轴器采用的润滑材料是（）。

A.复钙基脂

B.合成石墨钙基润滑脂

C.机械油

D.齿轮油