考研英语：历年真题阅读要点之1991-Text 3

　　C. R. Barnes has suggested that it is as proper to term the plant a water structure as to call a house composed mainly of brick a brick building.

　　suggest可以表示“认为”;it充当形式主语，真正的主语是to term the plant a water structure，也就是说，其实这个句子就是to term the plant a water structure is as proper as to call a house composed mainly of brick a brick building“称植物为水建筑和称主要由砖砌成的房子为砖建筑一样合适”;as...as...为比较结构;term“把...叫做”;be composed of“由...组成”。

　　Certain it is that all essential processes of plant growth and development occur in water.

　　正常语序it is certain that...其中，it充当形式主语，真正的主语是that引导的主语从句;certain提前，起到强调作用;essential“基本的，必要的”，常见搭配be essential to“对...必不可少”，比如Environmental protection is essential to social development.

　　The processes of photosynthesis, by which carbon dioxide and water are combined -- in the presence of chlorophyll and with energy derived from light -- to form sugars, require that carbon dioxide from the air enter the plant.

　　by which carbon dioxide and water are combined to form sugars为非限定性定语从句，充当插入语，起到补充说明的作用，可以略过，题干涉及另当别论;in the presence of chlorophyll and with energy derived from light为两个破折号之间的内容，同样充当插入语;也就是说，这个句子应该重点关注的内容是The processes of photosynthesis require that carbon dioxide from the air enter the plant.

　　42. The essential function of photosynthesis in terms of plant needs is ________.

　　[A] to form sugars

　　[B] to derive energy from light

　　[C] to preserve water(A)

　　[D] to combine carbon dioxide with water

　　题干涉及“就植物的需求而言，光合作用的基本功能。”也就是说，解题的时候，我们要返回原文，关注一下by which carbon dioxide and water are combined to form sugars这个插入语，“光合作用合成糖分”。结合上文The carbon dioxide (CO2) from the air may enter the leaf as a gas but is dissolved in water in the leaf before it is combined with a part of the water to form simple sugars -- the base material from which the plant body is mainly built.可知，本题选A。另外，各位同学精读的时候，不用关注文中出现的生僻词汇和专业术语，考查的可能性很小。