题目

---Which one would you like?   --- Of the two T-shirts，I’d choose the______one to save some money for a book．     A．cheapest            B．cheaper         C．more expensive   D．most expensive 答案：B已知，函数.（1）当时，讨论函数的单调性；（2）当有两个极值点（设为和）时，求证：.