21. You see, I still have this pain in my back; this medicine the doctor gave me was supposed to make me feel better by now.

点睛　

被动语态表示主动含义的用法在英语里很常见，但却与我们中国人的思维习惯相去甚远，考生需多加练习。分号后句子的意思是“医生给我开的药现在应该可以使我感觉好些了（意为说话人的症状现在未见好转）”。

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 students alike. 老师应该对所有学生一视同仁。
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. 到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。