the answer is A,tellme why ,why not use B
2个回答

the plan was difficult to carry out表示这个计划费尽千辛万苦才浮出水面,用主动表示其出现

the plan was difficult to be carried out 强调这个计划被他人实现,

be difficult/easy to do 是固定搭配 用主动表被动.

这里the plan was difficult to carry out更合适,更符合语境