题目

Younger adults who get either little sleep or a lot of it ________ see a greater expansion in their waistlines over time. A. may        B. must         D. need        D. shall 答案：A 解析: 略现在高1米，每年长高0.1米，请写出树高y（米）与时间x（年）之间的函数关系式：______．