to their own work ,most of the parents spend little time with their children.

A．Devoting

B．To be devoted

C．Having devoted

D．Devoted

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