有时风大流急，船舶靠码头时必须掉头顶流。（）

AA ship has to turn to stem the tide because the wind is strong when she is getting alongside a wharf.

BSometimes the wind is strong and the current is rough, so a ship has to turn to stem the tide when she is getting alongside a wharf.

CThe wind is big, a ship must get alongside a wharf so she has to turn to stem the tide.

DA ship has to turn to stem the tide so she can get alongside a wharf.