（1）构成进行时态：
I’ll be seeing her at 10 tomorrow. 我明天十点和她会面。
What have you been doing these days? 这些天来你在干什么？
（2）构成被动语态：
What has been assigned for today’s homework? 今天留了什么作业？
Preparations are being made for the speech contest. 演讲比赛的准备工作正在进行。
（3）和动词不定式构成复合谓语，表示按计划安排即将发生的事情：
A new hospital is to be built in our district. 我们区要修建一所新医院。
Where are we to meet? 我们在哪里碰头？