题目

 You can choose ______ food you like in our hotel.          A. some         B. many         C. a                       D. any 答案：D已知a＞0,函数f（x）=x3-a,x∈［0,+∞）,设x1＞0,记曲线y=f（x）在点M（x1,f（x1））处的切线l.（1）求l的方程;（2）设l与x轴交点为（x2,0）,证明:①x2≥ac；②若x1＞a,则a＜x2＜x1.