答案应该是A吧imagine sth to be=imagine sth as
Some people imagine flying to be more dangerous than travelling by train.Which is wrong.
to be more dangerous than travelling by train.用来说明flying（也就是宾补）说以说是复合宾语.
这是新概念3册内容
eg.we sometimes imagine a desert island to be a sort of paradise where the sun always shines.
我们有时想象荒岛是阳光终日普照的天堂.
to be a sort of paradise where the sun always shines就是用来说明宾语a desert island的情况,也就是宾语补语