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

作业时，起重机臂架、吊具、辅具、钢丝绳及吊物等与220kV架空输电线及其它带电体的最小安全距离是4.5m。