it is... that(强调句与定语从句的区别)

强调句(分裂句)中的 that(who)从句与充当定语的 that(who)从句在形式上是相同的，因此,有时候我们不经仔细分析就很难把它们区别开来。但是,既然它们是本质上不同的两种句型,我们就有办法把它们区分开来(参见 cleft sentence $^{4}$ )。

A. 从结构上看,强调句中 it is(was)... that 去掉之后,把语序稍加调整,句子结构和意义仍是完整的,而定语从句却不是这样:

1. It was a glass that Mary broke. (玛丽打碎的是一只玻璃杯。)→Mary broke a glass. (玛丽打碎了一只玻璃杯。)

2. It was a key that I found in his pocket. (我在他衣袋里找到的是一把钥匙。)→I found a key in his pocket. (我在他的衣袋里找到了一把钥匙。)

B. 在强调句中, it is (was) A that 中的 A 总是要译成被强调的成分, 而定语从句所修饰的名词 A 却不能翻译成被强调的成分:

1. It is novels that Miss Williams enjoys reading. (强调句) 威廉姆斯小姐喜欢读的是小说。

2. It is a question that needs careful consideration. (定语从句) 这是一个需要仔细考虑的问题。

按照上面所说的两点,我们能鉴别出你所提问的句子到底是强调句还是含定语从句的句子。

一、它不能取消 it must have been...that 而使句子的结构和意义保持完整：

It must have been a gas that could burn but that would not explode, a gas that did not smell strong, and a gas that did not kill people. $\rightarrow (\times)$ A gas could burn but would not explode, a gas did not smell strong, and a gas did not kill people.

改写后的句子无论在结构上,还是在意义上都是不完整的。请对比:

It must be my book that he is reading. (强调句)→He is reading my book. 他正在读的一定是我的书。