.It was not until he went abroad for further study______Li Ming realised the importance of English.

A．when

B．that

C．where

D．before

单斗拉铲挖土机的挖土特点是（）。

A．前进向上，强制切土

B．后退向下，强制切土

C．后退向下，自重切土

D．直上直下，自重切土