第27题: [单项选择]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 D. to combine carbon dioxide with water 参考答案:A 答案解析:[解析] 根据文章第二段第二句...derived from light-to form sugars可知,A项符合题意,其他几项均不准确。