磨煤机油系统正常运行维护项目有哪些？
参考答案：
油滤网差压高切换清理，维持正常油位，调整油温/油压，投入电加热和冷却水。
_____ makes his parents proud is _____ his son has been admitted by Beijing University.
A．That; because
B．That; what
C．What; that
D．What; because
内径千分尺可测量最小孔径为（）。
A.5mm
B.50mm
C.75mm
D.100mm
