Reserve buoyancy is the ().
A.Unoccupied space below the waterline
B.Volume of intact space above the waterline
C.Excess of the buoyant force over the gravity force
D.Difference in the buoyant force in salt and fresh waters

线路所车站值班员与后方站（线路所）办理区间开通手续前，必须确认（ ）空闲。

A.站间区间
B.所间区间
C.闭塞分区
D.接车进路

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The exhaust ports of a diesel engine using the cross-flow scavenging method are opened and closed by the _________.A.reciprocating motion of exhaust valvesB.rotary motion of the camshaftC.reciprocating motion of the pistonD.developed differential

A.
A.reciprocating
B.rotary
C.reciprocating
D.developed

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