When the plane is to take off has not been announced 飞机何时起飞还没有宣布为_英语解答

When the plane is to take off has not been announced 飞机何时起飞还没有宣布
为什么这边要使用 to take off又不能做谓语

人气：454 ℃　时间：2019-08-19 01:31:35

解答

When the plane is to take off 句子的主语这个是一个主语从句 is to 表示将来 be to do 表将要发生的事情