be supposed to的用法

用法一: be supposed to...其中to是动词不定式符号，不是介词，其后要跟动词原形。当be supposed to...的主语是“人”时，意为“应该....”;“被期望...，它可以用来表示劝告、建议、义务、责任等，相当于情态动词should。

用法二:当be supposed to... 的主语是“物”时，它表示“本应;本该”，用于表示“某事本应该发生而没有发生”。

如:

①The new laws are supposed toprevent crime.

这些新法令本应该起到防止犯罪的作用。②The train was supposed to arrive half an hour ago.

火车本应在半小时之前到达。

[典例分析]

You're not .to walk on the grass.We should learn to protect it.

A. supposed B. suppose C. supposing

[答案] A

考点:考查固定句式的用法。