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 In attributive clauses, prepositions can be added before the relative pronouns who, who, which, and whose, but prepositions must follow two principles. First, the prepositions before the relational pronouns must be collocated with the verbs of the clauses. Such as: 1.In the street, there wasn’ta single person to whomshe could turn forhelp.The street was empty and she could not ask for help. Turn to sb.forhelp