一、 be +
现在分词,构成进行时态。
1)They are having a meeting. 他们正在开会。
2)We were planting trees this time yesterday. 我们昨天这个时候在植树。
二、 be +
过去分词,构成
被动语态。
1)The door was broken by Tom. 门是汤姆打破的。
2)English is taught in our school. 我校教英语。
三、 be +
动词不定式,可表示:
1、 打算、决定、计划、安排等。
1) He is to visit Japan next week. 他决定下周访问日本。
2) I was to have told you yesterday, but you were not in.
我本打算昨天告诉你的,但你不在家。
2、 指示、命令、禁止等,即“必须,一定”。
1)You are to hand in the exercises tomorrow. 你们明天必须交练习。
2) You’re not to (=You mustn’t) smoke here. 你不可以在此处抽烟。
3、 责任、义务、需要,即“该不该”。
1)are to (=should) report to the police. 你应该报警的。
2)Am I to go on with the work? 这工作我该不该继续干下去?
4、 可能性,与can, may相当,不定式多用被动式。
1)The book was not to (=could not) be found. 那本书可能找不到了。
5、 假设,用于虚拟条件句中。
1)If it were to rain, we would get wet. 要是下雨,我们就会淋湿。
6、表示注定要发生或后来必然发生。
)experience was to change his life. 这次经历注定要改变他的生活。
注:不定式作
表语与上述用法是不同的。
1) My idea is to go there today. 我的意思是今天就去那里。