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。English is becoming more and more important. 英语现在越来越重要。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。English is taught throughout the world.世界各地都教英语。3) be + 动词不定式,可表示下列内容: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。We are to teach the freshpersons.我们要教新生。说明: 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。He is to come to the office this afternoon.要他今天下午来办公室。c.征求意见,例如:How am I to answer him?我该怎样答复他?Who is to go there?谁该去那儿呢?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。