建设在（）河床上的河道整治工程更是很大程度上靠护根维持稳定。
A.易冲刷
B.坚固
C.稳定
D.岩石
参考答案：A
It’s generous __ ___ them to donate money to UNICEF. They think it important _____ them to help poor children go to school.
A．to; for
B．for; of
C．of; to
D．of; for
简述真空泵的保养方法？
