关于一个过去将来时的英语句子的问题
将"He said they would take down the old building."改成被动语态．
书上的答案是：He said the old building would be take down by them.
可是过去将来时改成被动语态后的形式不是would be done吗?为什么答案中的take没有用过去分词的形式呢?