4. They lost their way, __B__ delayed them considerably.
A. as B. which C. that D. but
解析：是前面整个句子里说的事，影响了后面句子里说的结果，所以先行词是整个句子，后面是非限制行的定语从句，所以要用which前加逗号来引导。
八、倒装
英语句子根据主语和谓语的位置可以分为自然语序 (主语在前、谓语在后) 和倒装语序 (为了语法或修饰上的需要而把谓语移至主语之前)。倒装语序又可以根据谓语在主语前的情况分为部分倒装和全部倒装。部分倒装是指将谓语的一部分(如助动词或情态动词) 倒装至主语之前。全部倒装是指句子中没有助动词、情态动词或系动词be，而把整个谓语动词放到主语的前面。如：
1. Only recently __C__ to deal with the environmental problems.
A. something has done B. has something done.
C. has something been done D. something has been done
解析：以only引导的状语如果放在句首，后面的主句要进行部分倒装。类似的结构还有以 not only (注意but also后为正常语序) 开头的句子及以否定词no, not, never, hardly, seldom开头的句子等。
2. So little __A__ about chemistry that the lecture was completely beyond me.
A. did I know B. I had known C. did I knew D. I know
解析：在“so … that” (如此•••以至于) 句型中，若so提至句首，后面就要用部分倒装。
九、主谓 (主语、谓语) 一致
主谓一致是指谓语动词要与主语要求的语法形式相一致，要求动词的单复数要与主语匹配。主谓一致所遵循的原则有：语法形式一致、概念或意义一致(语言内容上一致)、邻近一致(谓语动词的单复数形式和邻近的主语相一致)。如：
1. Mr. Smith, together with his wife and children, __B__ going to the party this weekend.
A. am B. is C. are D. will
解析：主语后面如果用逗号，再和together with短语连用时，不要管 together with,真正的主语是 Mr. Smith；逗号在这儿的功能相当于表明，逗号后面是主语的补充说明成分，可有可无。类似的情况还有as well as, with, along with, like, rather than, except, but, including, accompanied, by, plus, besides, in addition to, no less than等在逗号后面加别的名词，做前面主语名次的补充说明成分。请看更多例句：
1. Every means __B__ been tried to solve the difficult problems.
A. have B. has C. is D. are
解析：有些名词形式上是负数，而意义上却是单数，如news, means等；还有许多以-ics结尾的学科名称，如economics, physics, mechanics, politics等，它们作主语时，谓语动词要用单数形式，因为这些名词本身是单数名词。
十、名词性从句
在句子中起名词作用的从句叫作名词从句，通常由从属连词that引导，也可由who, whom, whose, what, which, whoever, whatever, whichever等连接代词引导，还可由where, when, how, why等连接副词引导。名词性从句在复合句中能作主语、宾语、表语、同位语、介词宾语等，因此根据它在句中不同的语法功能，名词从句又可分别成为主语从句、宾语从句、表语从句和同位语从句。如：
1. Although Mary is satisfied with her success, she wonders __C__ will happen to her private life.
A. how B. who C. what D. that
解析：wonder后面为宾语从句，所以what与从句中的内容相符，表示“想知道什么”。
2. __A__ was once regarded as impossible has now become a reality.
A. What B. That C. Which D. As
解析：what在这里引导主语从句，即我们所说的 “what” 短语，代替了句中某个“事或物”，相当于中文里的 “曾经被认为不可能的 (人或事)”、 “说过的”、“看到的” 等，而这个“事或物”(名词) 则往往被省略或没必要具体指出。
3. All the evidence points to the fact __C__ he is the murder.
A. who B. which C. that D. those
解析：that在这里引导的是同位语从句。
十一、强调
常见的强调句型为：It is (was) + 被强调部分 + that (who) + 句子其他部分。此结构强调的成分仅限于主语、宾语和状语。强调句还有一种类型，就是用助动词do (did, does) 强调谓语。如：
It was not until she had arrived home __B__ remembered her appointment with the doctor.
A. when she B. that she C. and she D. she
解析：强调句式为 “it is/was … that …”。