不定式在句子中可以充当很多成分，如名词，形容词或副词：
◆ Noun: I love TO SWIM. To swim 作为love 的宾语.
◆ Adjective: The person TO MEET is here. To meet 修饰名词person .
◆ Adverb: Sue paused TO EAT lunch. To eat 修饰动词paused .
对于不定式的使用，我们也更应该关注不定式所要表达的目的：
Right: The contractors demolished the building TO KEEP it from falling down accidentally. demolished 的发起者是contractors ,同时也是不定式to keep的发起者，它描述了demolish 的目的，这里的it 指代building。
我们再看一个例子：
Wrong: The building was demolished TO AVOID falling down accidentally. 例子中building 本身不可能AVOID falling down，对于上面例子可以这样修改：The building was demolished TO KEEP IT from falling down accidentally. 这里的it 指代building ，经过这样修改，building 变成了不定式的宾语。不定式虽然可騨发名词用但还是和名词有许多不同的地方，比如不能作为介词的宾语。
下面我们就来练一道题目：
Australian embryologists have found evidence that suggests that the elephant is descended from an aquatic animal, and its trunk originally evolving as a kind of snorkel.
A that suggests that the elephant is descended from an aquatic animal, and its trunk originally evolving
B that has suggested the elephant descended from an aquatic animal, its trunk originally evolving
C suggesting that the elephant had descended from an aquatic animal with its trunk originally evolved
D to suggest that the elephant had descended from an aquatic animal and its trunk originally evolved
E to suggest that the elephant is descended from an aquatic animal and that its trunk originally evolved
解析：
A. Suggest that… and that…. 第二个that不能省略，且and前面不需要逗号
B. Suggest的用法不符合习语
C. 句子使用过去完成时没有根据，with部分结构错误
D. 宾语从句平行，第二个that不能省略
E. 正确
