昨天他们被要求打扫教室
这辆自行车是在天津制造的
主动句是Someone asked them to clean the classroom yesterday
Someone makes this kind of bike in Tianjin为什么是makes像someone/somebody/everyone/everybody/something/anything等不定代词作主语，谓语动词要用三单形式O(∩_∩)O~