B seems like the best choice.
they were already unreachable but archers helped too
Explanation:
In order to prevent an enemy getting over the wall the castle builders selected their site with great care so that the terrain would be difficult for a belfry to cross. They then made it more difficult by digging a ditch or moat around the curtain walls in order to prevent the towers getting close to the battlements. yet archers played a great role in middle ages by defended castles and kingdoms from top while infantry troops fought.
