首先，因果关系词，其实有两类，一个是表示原因的：as、since、thanks to、as result of、because of、owing to、result from、due to、on account of、by virtue of、in that、attribute to;另一个是表示结果的：as a consequence、thus、hence、so、as a result、result in、contribute to、lead to、cause、breed、trigger。

　　来分析一道句子插入题。句子插入题解题核心就在于要把待插入句子放在方框内，使得它能和上下文衔接得当。

　　如何做到上下文衔接得当?其一：句意。其二：逻辑。如果待插入句子中出现代词加名词短语，我们一定在原文中找到这个代词的指代;如果文中只有一处合适，答案就是那句话的后面;如果有两处以上符合，那么我们就观察一下这句话中有没有逻辑关系词，我们一定要确定这句话和上文逻辑关系正确。

　　Paragraph 6: ■Because they are always swimming, tunas simply have to open their mouths and water is forced in and over their gills. ■Accordingly, they have lost most of the muscles that other fishes use to suck in water and push it past the gills. ■In fact, tunas must swim to breathe. ■They must also keep swimming to keep from sinking, since most have largely or completely lost the swim bladder, the gas-filled sac that helps most other fish remain buoyant.

　　Look at the four squares [█] that indicate where the following sentence could be added to the passage.

　　Consequently, tunas do not need to suck in water.

　　Where would the sentence best fit?

　　带插入句子中出现名词：tuna，我们不难发现，这段就是围绕tuna来写的，所以考虑逻辑关系词：consequently，表明上文提到了原因，下文应该是吞拿鱼不吸水的后果。我们在第二个方框后看到accordingly，这个词也是表示结果，后面说到“他们丢失了大部分用于吸水的肌肉”，所以这道题很好做了，逻辑简单，肯定是不吸水在先，然后才会丢失肌肉，所以答案是B。