[A]The shellfish have a long history in the rock and many different kinds are known.
[B] Nevertheless, we know a great deal about many of them because their bones and shells have been preserved in the rocks as fossils. From them, we can tell their size and shape, how they walked, the kind of food they ate.
[C]The first animals with true backbones were fishes, first known in the rocks of 375 million years ago. About 300 million years ago the amphibians, the animals able to live both on land and in water, appeared. They were giant, sometimes 8 feet long, and many of them lived in the swampy pools in which our coal seam, or layer, formed. The amphibians gave rise to the reptiles and for nearly 150 million years these were the principal forms of life on land, in the sea, and in the air.
[D]The best index fossils tend to be marine creatures. These animals evolved rapidly and spread over large areas of the world.
[E]The earliest animals whose remains have been found were all very simple kinds and lived in the sea. Later forms are more complex, and among these are the sea-lilies, relations of the star-fishes, which had long arms and were attached by a long stalk to the sea bed, or to rocks.
[F]When an animal dies, the body, its bones, or shell, may often be carried away by streams into lakes or the sea and there get covered by mud. If the animal lived in the sea its body would probably sink and be covered with mud. More and more mud would fall upon it until the bones or shell become embedded and preserved.
[G]Many factors can influence how fossils are preserved in rocks. Remains of an organism may be replaced by minerals, dissolved by an acidic solution to leave only their impression, or simply reduced to a more stable form.
解题思路:
本文文章部分共332字,备选答案部分字数为317字,总数达649字。阅读如此长的文章并做对题,要求考生具有较强的阅读理解能力,掌握正确的阅读方法。
首先,通篇略读原文,把握要点词句(文中黑斜体部分为要点词句,以下同),以便对文章主旨、各段基本主题以及逻辑结构获得一个概括性了解。
第一段指出:在人类出现很早以前,地球上就出现了鱼类、爬行动物、鸟类和一些哺乳动物(这是对全文的一个概述,点出本文的话题)。虽然这些动物有一些是现今生活着的各种动物的祖先,但是另一些动物现在已经灭绝了,即它们现在已经没有活着的后代了。第二句是个表示让步关系的句子,重点是主句部分:others are now extinct, that is, they have no descendants alive now,而that is表明they have no descendants alive now是同位语结构,因此本段要点词语为others are now extinct。这为回答第41题从意思和逻辑上都提供了主要依据。
第二段首句指出:偶尔根据石头里所显示出来的印记,我们可以合理地推断出几百万年前灭绝了的某种动物的准确形状,尽管不能确定其颜色。此句前后是因果关系,提到了rocks,结果是so that…we can build up…picture。后面又接着讲rocks in which the remains are found。由此可知,这些是本段的要点词语。
第三段中已知信息是:我们所知道的所有化石几乎都是由于水的作用而被保存在了石头中,而且大多都是生活在水里或水边的动物。因此,肯定存在过许多我们一无所知的哺乳动物、鸟类和昆虫类。空白后第一句是个并列句,主语分别是Nearly all of the fossils和 most of these (the fossils),而且都与water action有关。这为回答第42题提供了主要线索。
第四段中提供的信息是:还有像螃蟹一样的动物,其身体表面是一层角状物。接下来此段详细介绍了这类动物的外貌特征。此处要点词语是also和crab-like creatures,说明上一句也在描述某种海生物。这为回答第43题提供了主要线索。
第五段空白后第一句中有指代词of these,these必定指代前文提到的复数名词。紧接着提到的ammonites是“这些贝壳类动物”的一种。后面有对它的描述:ammonites非常有趣而又很重要。它们身体上有个由许多腔室构成的硬壳(shell),每个腔室都代表着这个动物的临时住所。这样,上一句提到的自然应该与贝壳类动物有关,为回答第44题提供了线索。
第45题为一段。下一段提到,大约7 500万年前,爬行动物时代结束了,其中大部分物种都灭绝了。而哺乳动物迅速发展起来,我们可以追寻出许多踪迹,借此了解许多大家熟悉的动物如大象和马的进化过程。后来的许多哺乳动物,虽然现在已经灭绝了,还是被原始人类所了解,并被画在了壁画中或被雕刻在了骨头上。注意本段第一句提到reptiles。由此我们推断上一段结尾处谈的内容必定与reptiles有关。这为回答第45题提供了主要线索。另外,最后一段第一句提到了年代,而选择项C中提到了几个年代,说明这里在按历史时序叙述动物的进化过程。
通过这样阅读全文要点信息,我们知道了本文结构的脉络:首先介绍什么是史前动物和人们研究史前动物的依据——化石,以及化石的形成过程。随后,作者按照动物进化的顺序(最早的动物,水生壳类动物,脊椎类动物等)逐一加以介绍。
当然,根据段落意思、句意和逻辑关系考查正确答案仅仅是可利用的手段之一,虽然它们提供了主要线索。考生还应该学会对词语线索的考查,以确保选出的答案在意思和用词上都与上下文衔接紧凑。有关重点词(包括相关代词、连词、名词或名词短语、动词等)已在原文中用斜体涂黑标出,这里暂且不作具体分析。总之,做题时要十分注意空白前后的句子,仔细分析句与句之间的关系,段与段之间的过渡衔接,根据上下文内容线索、逻辑关系、词语线索等,来判断每个题的正确答案。