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.