1. 考查which引导的非限制性定语从句
which引导非限制性定语从句，用以指代整个主句的内容，或主句中某个词或短语的内容。如：
(1) By serving others, a person focuses on someone other than himself or herself, _______ can be very eye-opening and rewarding.
A. who B. which C. what D. that
答案为B。which在此引导非限制性定语从句，which在定语从句中用作主语，表示前面所提到的情况。
(2) Chan’s restaurant on Baker Street, _______ used to be poorly run, is now a successful business.
A. that B. which C. who D. where
答案为B。which used to be poorly run为非限制性定语从句，其中的which指代前面的China’s restaurant。
2. 考查as引导的非限制性定语从句
as也可指代整个主句的内容，但不同于which的是，它引导的定语从句既可以位于主句的前面，也可以位于主句的后面。它的意思是“正如”，在这些从句中as 作主语或宾语。如：
(1) _______ I explained on the phone, your request will be considered at the next meeting.
A. When B. After C. As D. Since
答案为。as 引导定语从句，其意为“正如”。
(2) _______ is often the case, we have worked out the production plan.
A. Which B. When C. What D. As
答案为D。解析：引导非限制性定语从句且位于主句之前，用as引导。答案分别为CBD。
3. 考查由“介词＋关系代词”引导的定语从句
“介词+关系代词”结构中的关系代词主要是which或whom，不能是that；其中的介词则要根据句子中的相关搭配来确定。如：
(1) He was educated at the local high school, _______ he went on to Beijing University.
A. after which B. after that C. in which D. in that
答案为A。after which中的which指“他在当地一所高中接受教育”，after which的意思就是“在当地一所高中接受完教育之后(即高中毕业之后)”。
(2) She was educated at Beijing University, _______ she went on to have her advanced study abroad.
A. after which B. from which C. from that D. after that
答案为A。after which在此引导非限制性定语从句，相当于and after that。又如：This I did at nine o’clock, after which I sat reading the paper. 九点时我做这件事，之后我就坐在那里看报。