钻井泵的阀盖、缸盖螺纹每（）清洗一次，并涂抹钙基润滑脂。
A.8h
B.l2h
C.24h
D.168h
参考答案：D
.This summer she took a training course, which was to help people develop their reading skills.
A．operated
B．devoted
C．designed
D．furnished
加热拆卸叶轮后，必须用保温被包好，使其均匀冷却防止变形（）
