每()个工作小时,要对发动机的保护装置检查。
A.1000
B.2000
C.3000
D.4000
参考答案:D
_ I feel tired and weak.
_ Why not stop ________.[ ]
A. to work
B. to have a rest
C. having a rest
D. to go on with your work
以下石材为火成岩的是( )。
A.大理石
B.石灰岩
C.花岗岩
D.石英岩