忌“多”—— 忌在定语从句中加入多余的宾语，如：
　　a . 误： Theemail that (which) I
　　received it yesterday was from Dr. Smith .
　　正： The email that (which) I received yesterday was from Dr .Smith .
　　b.误：Are these the words you
　　wrote them just now?
　　正：Are these the words you wrote just now?
　　简析：例a中误句的that(which)在从句中做received的宾语，it是多余的词。 例b中误句的关系代词that (which)已经被省略， that(which)作wrote的宾语，them属于多余,应该去掉。
　　忌“漏”—— 忌遗漏在定语从句中做主语的关系代词，如：
　　a. 误：This is the thief stole my car.
　　正：This is the thief who / that stole my car.
　　简析：应该在句中的thief后加上who / that，关系代词who / that在从句中做主语。
　　b. 误：The boy often comes late to school was ill last week.
　　正：The boy who / that often comes late to school was ill last week.
　　简析：在boy 后面加上who / that，这里who / that在定语从句中做comes的主语。
　　忌“误”—— 忌在定语从句中谓语动词的单、复数误用，如：
　　a. 误：Those who has got the apples can leave here now.
　　正：Those who have got the apples can leave here now.
　　简析：句中的who指代those, 从句中谓语应用复数形式，所以has应该改为have。
　　b. 误：She is one of the girl students who is good at swimming.
　　正：She is one of the girl students who are good at swimming.
　　简析：句中who指girl students，句子的意思是“她是擅长游泳的女学生之一”，故谓语动词is应改为are。
　　忌“重”—— 忌在定语从句中介词重复使用，如：
　　误：The flat where Mrs Black lives in is mine.
　　正：The flat where Mrs Black lives is mine.
　　或The flat （which）Mrs Black lives in is mine.
　　简析：误句中的where = in which,再加上介词in，显然是重复的。
　　忌“混”—— 忌在定语从句中关系代词（which / that）与关系副词(when / where)混用，如：
　　误：I’ll never forget the day when we spent together.
　　正：I’ll never forget the day which / that we spent together.
　　简析：误句中when应该改为which / that, 因为which / that在从句中做spent的宾语，而when做从句的状语。