四个选择答案中,b是正确的答案。 a句是错误的,它与b句的不同,在于前者用逗号把从句和主句的主谓部分隔开,是非限制性的定语从名;后者不用逗号,是限制性定语从句。限制性定语从句和非限制性定语从句所表示的概念和用法上都不相同,其中很重要的一点区别是;限制性定语从句用来限制先行词,使它指的是同类人或事物中的一些或部分;非限制性定语从句则只是用来对修饰的名词作进一步说明,指的是同类人或事物中的全体。试比较: Of the four choice answers, b is the correct answer. A sentence is wrong. It differs from sentence b in that the former separates the clause from the subject-predicate part of the main sentence with a comma. It is an unqualified adverbial name; the latter does not use a comma, but is a restrictive attributive clause. The concept and usage expressed by the restrictive attributive clause and the non-restrictive attributive clause are all different. The important difference is that the restrictive attributive clause is used to limit the antecedent to make it refer to the same kind of person or thing. Some or all of them; non-restrictive attributive clauses are only used to further explain the modified nouns, referring to the whole person in the same category or things. Try to compare: