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be supposed to do的用法
be supposed to do在本单元中是“应该；被期望；理应”之意。用来表示
根据规定，人们不得不做的事，或期待发生的事。
时态、人称和句式的变化在be动词上体现，to为不定式符号，后接动词原
形。
其用法如下：
1.be supposed to do的肯定句式 be supposed to do的肯定句式，be动
词随主语的变化而变化，to后接动词原形。
例句：You're supposed to start work at 8:30 every morning. 你应该每
天早晨8：30开始工作。
The train was supposed to arrive half an hour ago. 火车本应该在半
小时之前到达。
2.be supposed to do的否定句式
be supposed to do的否定句式即在be动词后加否定词not，此时相当于
be not allowed to do, 意为“不被许可；不应当”。
例句：We are not supposed to play football in the street. 我们不应该
在大街上踢足球。
It is a secret still. I am not supposed to say it out. 这还是个秘密，我
不能说出来。
3.be supposed to do的疑问句式
be supposed to do的疑问句式需将be的相应形式提到主语前。
例句：Is he supposed to get there at five? 他应该在五点钟到那儿吗？Was Lucy supposed to speak Chinese like that? 露西应该像那样说汉
语吗？
（1）当be supposed to…的主语是“人”时，意为“应该；被期望……”，
此时可以用来表示劝告、建议、义务、责任等，相当于情态动词should。
例句：You're supposed to tell him if you want to leave. 如果你要离开，
应该先告诉他。
（2）当be supposed to…的主语是“物”时，意为“本应；本该”，用于表
示某事本应该发生而没发生。
例句：The meeting is supposed to take place on Tuesday, but we
have to put it off. 这次会议本应在星期二举行，但我们不得不把它推迟。
