44)____Of these, the ammonites are very interesting and important .They have a shell composed of many chambers , each representing a temporary home of the animal .As the young grew larger it grew a new chamber and sealed off the previous one .Thousands of these can be seen in the rocks on the Dorset Coast .

　　45)____ About 75 million years ago the Age of Reptiles was over and most of the groups died out .The mammals quickly developed, and we can trace the evolution of many familiar animals such as the elephant and horse . Many of the later mammals though now extinct ,were known to primitive man and were featured by him in cave paintings and on bone carvings .

　　[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 the 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 ,or 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 creature .There animals evolved rapidly and spread over large 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 forma 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 up 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 .

　　本篇介绍的是史前类动物。文章结构的脉络清晰：首先介绍什么是史前动物和我们研究史前动物的依据——化石，以及化石形成的过程。随后，作者即按照动物进化的顺序——我们可以见到其化石的最早的动物，水生壳类动物，脊椎类动物——逐一加以介绍。

　　41．文章一开始，作者告诉我们，早在人类出现以前地球上就许多物种，现在有些物种的后代依然生存，而另外一些则没有留下后裔。在本题空白处后面文章又说岩石上偶尔会留下数百万年前就死掉了的动物精确的印记。显然，空白处应该是关于岩石与灭绝了的动物之间的关系（7个选项中有A﹑B﹑E﹑G四项提到了“rock”,但另外大三项意思上不符）。此外，空白处前面的“extinct”和“no descendant”均为否定意义和表达，而空白处的后面“accurate”和“much”则为肯定意义的表达；这意味着空白处的内容应该有一个结构上的“转折—只有B项符合这一条件。所以正确答案只能是B。