2、摒弃 There be 句型!
Botany, the study of plants, occupies a peculiar position in the history of human knowledge.(陈述句，同位语，下定义)
For many thousands of years it was the one field of awareness about which humans had anything more than the vaguest of insights.(时间状语开头)
It is impossible to know today just what our Stone Age ancestors knewabout plants, but from what we can observe of pre-industrial societies that still exist, a detailed learning of plants and heir properties must be extremely ancient.
This is logical.(长短结合)
Plants are the basis of the food pyramid for all living things, even for other plants. They have always been enormously important to the welfare of people, not only for food, but also for clothing, weapons, tool, dyes, medicines, shelter, and a great many other purposes.(递进句型，排比)
Tribes living today in the jungles of the Amazon recognize literally hundreds of plants and know many properties of each. To them, botany, as such, has no name and is probably not even recognized as a special branch of “knowledge” at all.(插入语，介词开头)。
Adj. Basic to any understanding of Canada after World War II is its impressive population’s growth.
Adv. Too, often, students are forced to cheat on tests.
Prep. From the shortage arises the demand for nuclear poweras a newsource of energy.
名词性从句 What was needed in reality was not taught in school.
1、he or she ，不过出现次数太多会很累赘
2、能用 they 就别用 he or she