引起采煤机液压牵引部过热的原因是()。
A、液压系统油质不符合要求
B、牵引速度较慢
C、冷却水量、水压不足
D、无冷却水
E、液压系统有外泄漏
参考答案:A, C, D, E
IBM小型机能安装Windows操作系统吗?
— Did you know any Chinese before you arrived in Beijing?
— Never ________ it, actually.
A.had I learned
B.have I learned
C.I have learned
D.I had learned