4)All ______ is a continuous supply of the basic necessities of life.
A. which is needed
B. that is needed
C. what is needed
D. is needed
正确答案是：B 注意：all that = what， 不可能出现all what
5) Some of the roads have been flooded(淹没)， ______ our journey more difficult.
A. it makes
B. they make
C. which makes
D. which make
解题思路：四个答题中有两个区分点：第一个区分点是：C、D都用了连接词"which"，而A、B没有用，根据"逗号不能连接两个句子"的原则，A、B肯定不对；第二个区分点是：C、D中，动词一个用单数形式makes，一个用复数形式，这里应选择C.为什么？非限制性定语从句中，除了说明先行的某个名词外，还可以说明整个句子的内容，此时动词用单数形式。全句意思：有的路已被洪水淹没，这使我们的旅行更加困难。"which"代表"有的路已被洪水淹没"这件事情。
考试时，当出现类似形式的题目而确实又看不懂句子意思时，应倾向于选择which 单数动词的那个选项。
6)They have made another wonderful discovery， ______ of great importance to science.
A. which I think is
B. I think which is
C. which I think it is
D. I think of which is
解题思路：英语中的连接词一般都是放在从句的最前面，据此，可以排除B、D选项；A、C的区分点是"it"， 想一下本节的第一题，就能正确选择答案A了。此类题目中，I think应理解为"插入语"，要熟悉这种形式，
又如：
He is the man ______ I suppose is capable of finishing this task.
该题应填who而不是whom
(在从句中)当状语时：关系副词where及when