The Master of a vessel berthed,moored or anchored within the area of jurisdiction and who
A. shall not request permission
B. shall request permission
C. shall,if in convenience,request permission
D. shall send his permission to the Harbour Master
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对高压设备发生火灾时应先操作隔离开关,后操作油断路器。()
螺旋桨的螺距与其______的比值称为螺距比。
A. 直径
B. 半径
C. 0.7倍直径
D. 0.7倍半径