【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.
4.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.
当时在CD之间选，觉得两个都对，请问C错在哪里了？是因为although?C是不是把前面一句的内容也包含进去了，所以错？作者: 君嘎幽灵 时间: 2014-11-27 14:56:01
