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

B、Sometimes 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.

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

D、A ship has to turn to stem the tide so she can get alongside a wharf.