托福阅读文章各个段落的主旨句一般是在每段的第一句话，后面的内容都是在对这个主旨句的解释说明，因此明白了这个句间关系，对于把握段落所讲内容和快速阅读文章有很大的帮助，前提条件是确定每个句子是如何具体来解释这个主旨句的。下面我们来看两个段落来分析一下。
The subjects of the paintings are mostly animals. The paintings rest on bare walls, with no backdrops or environmental trappings. Perhaps, like many contemporary peoples, Upper Paleolithic men and women believed that the drawing of a human image could cause death or injury, and if that were indeed their belief, it might explain why human figures are rarely depicted in cave art. Another explanation for the focus on animals might be that these people sought to improve their luck at hunting. This theory is suggested by evidence of chips in the painted figures, perhaps made by spears thrown at the drawings. But if improving their hunting luck was the chief motivation for the paintings, it is difficult to explain why only a few show signs of having been speared. Perhaps the paintings were inspired by the need to increase the supply of animals. Cave art seems to have reached a peak toward the end of the Upper Paleolithic period, when the herds of game were decreasing.
段落的第一句话说画的对象主要是动物，这是这个段落的主旨句，第二句是来解释为什么动物是主要的画的对象，可能是因为他们认为人物画会造成死伤，所以他们主要画动物。第二个解释是发现有的画有被矛刺过的裂痕，来说明他们可能是为了提高打猎是的运气，在画上练习，来说明为什么画的大部分是动物，因为是他们要练习打猎，提高命中率。第三个解释说是为了提高动物的供给，因为发现当猎物减少的时候，动物画到达了顶峰，没有什么就画什么想得到什么，这是对画的主要对象是动物的一个解释。整个段落就是对这个主旨句的解释，明白了这个，我们对于托福阅读试题中的小结题这个段落的主要内容就很容易选择了。
Watt's steam engine soon showed what it could do. It liberated industry from dependence on running water. The engine eliminated water in the mines by driving efficient pumps, which made possible deeper and deeper mining. The ready availability of coal inspired William Murdoch during the 1790s to develop the first new form of nighttime illumination to be discovered in a millennium and a half. Coal gas rivaled smoky oil lamps and flickering candles, and early in the new century, well-to-do Londoners grew accustomed to gaslit houses and even streets. Iron manufacturers, which had starved for fuel while depending on charcoal, also benefited from ever-increasing supplies of coal: blast furnaces with steam-powered bellows turned out more iron and steel for the new machinery. Steam became the motive force of the Industrial Revolution as coal and iron ore were the raw materials.
这个段落的第一句话说瓦特的蒸汽机很快就表现出他能做什么，这是这个托福阅读段落的主旨句，我们来看下面是怎么解释这个观点的，第一个是他把工业从对流水的依赖上解放出来，使得煤挖的更深，这是一个影响。第二个是他的蒸汽机激发了WM这个人发明了夜间照明系统。第三个是铁的制造者也受益了。这是这个段落的句间演绎，题目中的第7题，问作者提到WM发明的夜间照明系统是为了说明什么，通过对于句间关系解释这个分析的运用，目的就很明确，是为了说明瓦特的蒸汽机能干，激发了WM去思考发明这个夜间照明系统。
通过这两个段落的句间关系之解释的分析，对于每个段落的主要内容，如何快速抓取和验证对于整个文章的阅读理解和速度的提高是很大的帮助。
上面介绍的这些托福阅读文章中句子的解析方法其实并没有那么难，研究和总结过托福阅读试题的同学可能都有体会，希望这能帮助大家的托福阅读有进步。