只需三招终结托福考试中的长难句

If the pores are large, the water in them will exist as drops too heavy for surface tension to hold, and it will drain away; but if the pores are small enough, the water in them will exist as thin films, too light to overcome the force of surface tension holding them in place; then the water will be firmly held。

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information。

首先我们先要判断一下这个句子是什么句类。根据句子的意思和句中出现的分号，我们可以判断出这是一个复杂句。

然后我们就来找各个分句间的主干和逻辑关系。读过这句话之后之后我们可以得知这句话的分句讲到了孔大和孔小两种情况。又因为有一个but存在，所以可以判断 两个分句间的逻辑应该是转折关系。那么下面我们就要读出转折的转的是什么。这句话的意思是：如果孔很大，水就会作为水滴存在;但是如果孔很小，水就作为薄 膜存在。可见，转折的内容是大孔和小孔，水滴和薄膜之间的对比。

在判断句类和找到主干、逻辑关系后，我们就来看一下选项。如果选项主干和逻辑齐全，就是正确选项。其余都是错的。

A. Surface tension is not strong enough to retain drops of water in rocks with large pores but it strong enough to hold on to thin films of water in rocks with small pores。

B. Water in rocks is held in place by large pores and drains away from small size pores through surface tension。

C. Small pores and large pores both interact with surface tension to determine whether a rock will hold water as heavy drops or as a thin film。