Regarding a Diesel engine crankcase, the general arrangement and installation should preclude the possibility of ()
A. free entry of air to the crankcase
B. water entering the crankcase while engine wash-downs are being performed
C. excessive oil leakage during periods of increased blow-by
D. sub-cooling internal component
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接地线必须和任何导线完全()和(),且仅能与建筑物的真正接地线或单独地网相连接。
对外营业机构运营主管由该机构的上级管辖行委派,运营主管的工作直接对受派机构负责。
A. 正确
B. 错误
请写出5种宝石学中的特殊光学现象,并分别解释其形成原因。
工业污水直排会污染水体,我们的生活污水直接流入河中,对水没什么污染,这种说法()
A. 对
B. 错