题目

--- How do you find Mr Li’s lecture?    --- Good indeed. It_______ many problems we have come across in our study.    A. says                       B. talks                     C. covers                  D. refers 答案：C 解析: 略设函数，a为实数，求函数的单调区间；若存在实数a，使得对任意恒成立，求实数m的取值范围．提示：