【托福阅读题型：Fossil Preservation句子简化题】托福阅读中句子简化题是重要题型之一。根据托福阅读题型不同来进行专项练习，是短期提高托福阅读能力的有效方法。同学们需要多加练习哦!

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　　托福阅读句子简化题：Fossil Preservation

　　【Paragraph 2】The term "fossil" often implies petrifaction, literally a transformation into stone. After the death of an　organism, the soft tissue is ordinarily consumed by scavengers and bacteria. The empty shell of a snail or clam may be　　left behind, and if it is sufficiently durable and resistant to dissolution, it may remain basically unchanged for a long period　　of time. Indeed, unaltered shells of marine invertebrates are known from deposits over 100 million years old. In many　marine creatures, however, the skeleton is composed of a mineral variety of calcium carbonate called aragonite.　Although aragonite has the same composition as the more familiar mineral known as calcite, it has a different crystal　form, is relatively unstable, and in time changes to the more stable calcite.(Fossil Preservation)

　　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.

　　○ When snail or clam shells are left behind, they must be empty in order to remain durable and resist dissolution.

　　○ Although snail and clam shells are durable and resist dissolving, over time they slowly begin to change.

　　○ Although the soft parts of snails or clams dissolve quickly, their hard shells resist dissolution for a long time.

　　○ Empty snail or clam shells that are strong enough not to dissolve may stay in their original state for a long time.