24. They are supposed to be here by now.

点睛

被动语态在英语里使用频繁，通常表示主动含义，这与中国人的思维习惯相去甚远，考生须多加练习。这句话的意思是“他们现在应该到这儿了。”

考点归纳

be supposed to的用法如下：
当be supposed to的主语是sb.时，意为“应该；被期望”，可以用来表示劝告、建议、义务、责任等，相当于情态动词should。如：
Teachers are supposed to treat all the students alike. 老师应该对所有的学生一视同仁。
当be supposed to的主语是sth.时，意为“本应，本该”，用于表示“某事本应该发生而没有发生”。如：
The train was supposed to arrive an hour ago. 火车本应在一小时之前到达。
当be supposed to后接“have＋过去分词”时，表示“本应该做某事而没做”。如：
You are supposed to have handed in your homework by now. 现在你应该已经把作业交上来了。
be supposed to的否定结构为be not supposed to，常用于口语中，意为“不被许可；不应当”。如：
She was not supposed to be angry about that. 她本不该为那件事而生气的。