可以,构成进行时或被动语态,此时的BE是助动词.
如:He is singing.
They were playing basketball at this time yesterday.
The bridge was built last year.
The book was borrowed by Liling yesterday.
1.be +现在分词，构成进行时态，例如：
They are having a meeting.他们正在开会。
2.be+过去分词，构成被动语态，例如：
The window was broken by Tom.窗户是汤姆打碎的。
3.be+动词不定式
a，表示最近、未来的计划或安排，
例如：
He is to go to New York next week.他下周要去纽约。
这种用法也可以说成是一种将来时态表达法。
b.表示命令，
例如：
You are to explain this.对此你要做出解释。
c.征求意见，
例如：
How am I to answer him?我该怎样答复他？
d.表示相约、商定，
例如：
We are to meet at the school gate at seven tomorrow morning.我们明天早晨7点在校门口集合。
