正确答案: D

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题目：生态学成为一门独立的学科的原因是由于（ ）

解析：D

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学习资料的答案和解析：

[单选题]下列加点虚词用法相同的两项是 （ ）①乃召绰，告之以事，绰即为量定

②④

[单选题]Passage FiveIn the United States, it is important to be on time, or punctual, for an appointment, a class, etc. However, this may not be true in all countries. An American professor discovered this difference while teaching a class in a Brazilian (巴西的) university. The two-hour class was scheduled' to begin at 10

being on time

解析：

51．答案为D  根据文章第一句it is important to be on time，or punctual可知punctual的意思是“守时”。

[单选题]Cleaners and farmers do ______scientists do.

as important work as

解析：47．答案为D  此题为推断题。从第三段中句子We can live without education，but we die if we have no food．和If no one cleaned our streets...we would have terrible diseases in our towns．我们可以推断出清洁工、农民和教授的工作同等重要。

[单选题]1798年马尔萨斯出版的一部对“生存竞争”和“物种形成”理论有重要影响的书是（ ）

《人口论》

[单选题]绘画中的画布、画笔、水墨在艺术品的层次结构中属于_________ ( )

物质实在层