The hole in the ground was three feet deep, making it difficult, if not impossible, _____the bus out.[ ]

A. getting

B. get

C. to get

D. got

标记为螺钉GB/T71—1985M5×12-14H中的14H即为螺钉的（）。

A.公称直径

B.公差代号

C.性能等级

D.材料牌号