His idea,though good,needs _out.答案是“to be tried”,但为什么不能是“being tried”

问题描述:

His idea,though good,needs _out.答案是“to be tried”,但为什么不能是“being tried”
这原是单选题

表示需要被做的两种表达:
sth need doing 
sth need to be done
所以need being doneg不好.