在定语从句中,关系代词whom,which,whose之前可加介词,但加介词必须遵循两条原则。一、搭配原则关系代词前的介词必须和从句的动词形成搭配关系。如:1.In the street,there wasn’ta single person to whomshe could turn forhelp.街上空无一人,她无法求助。turn to sb.forhelp是“求助某人”的意思,在句中介词to和turn形成搭配关系。2.H e m ade another wonderful discovery,of which isgreatim portance to science.他又一次惊人的发现对科学具有重要意义。isof意为“具有”,介词of和is构成搭配关系。3.H e lived in a cottage,in which Lincoln once lived.他住在林肯曾住过的小木屋里。介词in和从句动词live形成搭配关系。二、取义原则关系代词前的介词和从句的动词无搭配关系,只能根据上下文取其意义,再决定介词。如:1.The scientistm ade a specialtelescope thr...