眾所周知, 定語從句可以分為限制性定語從句和非限制性定語從句。下面結合考例談談學習運用非限制性定語從句時應注意的幾個問題：
一、that不能用來引導非限制性定語從句。如：
【考例一】She heard the terrible noise, ________brought her heart into her mouth.
A. it B. which C. this D. that
【解析】選B。后半句為非限制性定語從句，盡管先行詞noise屬于事物，也不能用that而要用which來引導。which指代noise，在從句中作主語。
二、除which外，還可用when，where，whose，whom等引導非限制性定語從句，且各自的用法及差異與它們用在限制性定語從句時相同。如：
Next month, when you'll spend your summer holidays in your hometown, is approaching. 下個月即將來臨，屆時你們將在家鄉度暑假。(關系副詞when指代表示時間的名詞next month，并作從句的狀語。)
She is going to live in Macao, where she has some close friends. 她要到澳門去居住，在那里她有幾個密友。 (關系副詞where指代表示地點的名詞Macao，并在從句中作狀語。)
【考例二】Recently I bought an ancient Chinese vase, ________was very reasonable.
A. which price
B. the price of which
C. its price
D. the price of whose
【解析】選B。whose在從句中作表示所屬關系的定語，既可指代人，也可指代物。指物時，常可轉換為of which；指人時常可轉換為of whom。
【考例三】 In the office I never seem to have time until after 5:30 pm,______many people have gone home.
A. whose time B. that
C. on which D. by which time
【解析】 先行詞5:30 pm與time之間是一種同位關系，可用which來作定語替代。從句中的完成狀態，常與by短語連用。故選D。
三、在非限制性定語從句中作賓語的關系代詞不能省略。如：
He was eager to go to the hospital to see his stepmother, whom he loved as his own mother. 他迫切地想到醫院去看望他的繼母，他把繼母當自己的親媽媽一樣愛戴。
四、非限制性定語從句的關系代詞which，既可以指代前面的先行詞，也可以指代前面整句的含義。如：
【考例四】 Dorothy was always speaking highly of her role in the play, of course,________made the others unhappy.
A. who B. which
C. this D. what
【解析】選B。指代“Dorothy總是高度評價自己在那場戲中所擔任的角色”的整個事件。
【考例五】Carol said the work would be done by October,________personally I doubt very much.
A. it B. that
C. when D. which
【解析】表示時間的名詞October，用“我個人非常懷疑”來修飾，意思不通。應該修飾整個主句， 表示對“Carol說在十月前能做好這項工作”懷疑。故選D。
五、引導非限制性定語從句時as和which的差異：從句置于句首時，非限制性定語從句只能用as引導，而置于句末時，兩者都可以使用。 如：
【考例六】________is known to everybody, the moon travels round the earth once every month.
A. It B. As C. That D. What
【解析】逗號表明為非限制性定語從句。選B。
【考例七】________is mentioned above, the number of the students in senior high schools is increasing.
A. Which B. As
C. That D. It
【解析】答案為B。與考例六同理。
文/彭昊虹