题目

Dear Mrs. Smith,                                         I was a student of yours in Grade Six, and I hope you still remember me. I'm writing this letter because I want to let you know that the school year with you was important and special time. It made a big contribution to my life. I know I was very quiet in your class, and you never said much to me. But you did something that made a big difference in my life. You see, all through my first years in schools, I hated to read. Books were just words that had very little to do with me, and I was bor产品的总成本y（万元）与产量x（台）之间的函数关系式是y=3000+20x-0.1x2，x∈（0，240）．若每台产品的售价为25万元，则生产者不亏本时（销售收入不小于总成本）的最低产量是（ ）A．100台B．120台C．150台D．180台