There are over 58, 000 rocky objects in _______ space, about 900 of  which could fall down onto _______ earth.

A．the; the

B．不填; the

C．the; 不填

D．a; the

现代车悬架系统中常加用扭力杆，主要作用是（）

A.代替减震器

B.加强减震器

C.代替平衡杆

D.辅助弹簧减缓冲击