问答题 Unfortunately the changes of any animal become a fossil are not very great, and
【正确答案】become becoming
【答案解析】[解析] 该句主句是The chances are not very great。因此become不能用原形，只能用现在分词形式表补充说明。
问答题
the chances of a fossil then being discovered many thousand of years later are even less.
【正确答案】thousand thousands
【答案解析】[解析] 短语thousands of years意为“数千年”。
问答题 It is not surprising that all the millions of animals that have lived in the past.
【正确答案】(of)all
【答案解析】[解析] of all the millions of animals意为“在数百万种的所有动物中”。
问答题
we actually have fossils of only very few.
【正确答案】(only)a(very)
【答案解析】[解析] only a few“仅仅少数，一点点”，句子中插入了“very”，置于“a”和“few” 之间。
问答题 There are several ways into which animals and plants may become fossilized.
【正确答案】into in
【答案解析】[解析] in this way意为“以这种方式”。
问答题First, it is essential that the remains are buried, as though dead animals and plants are quickly destroyed
【正确答案】though
【答案解析】[解析] though虽然，尽管；as though好像，仿佛。删除though。
问答题if they remain exposed the air. Plants rot, while insects and hyenas cat the flesh and bones of animals.
【正确答案】(exposed)to(the)
【答案解析】[解析] expose的常见搭配是expose oneself to和be exposed to。exposed to the air意为“暴露在空气中”。
问答题Finally, the few remaining bones soon disintegrate the hot sun and pouring rain. If buried in suitable conditions, however, animal and plant remains will be preserved.
【正确答案】(disintegrate)in(the)
【答案解析】[解析] in the sun意为“在阳光下”。
问答题The same chemicals change sand and silt into hard rock will also enter the animal and plant remains and make them hard too.
【正确答案】(chemicals)that(change)
【答案解析】[解析] 本句主句是The same chemicals will also…chemicals后不能跟动词，要么改为从句，要么改成现在分词形式；因为分词形式与语意不是很符合，所以此处用从句较合适。
问答题When this happens, we say that they become fossilized.