题目

阅读短文，选择最佳答案。 Darning is a Chinese boy. He is very helpful. Yesterday was Sunday. He had no classes. He was very excited yesterday, because his family had a picnic in a Park. Darming got up at 6 o'clock in the morning. He cooked breakfast for his parents. They went to the park by car. In the park. Daming played with his dog and ate food. Then he flew a kite. The kite flew higher and higher. They were very happy. At 4 o'clock, they went back home. In the evening, Daming watched TV with his parents. Yesterday was a nice day. （1） Is Darning an English boy or a 某蔬菜基地种植西红杮，由历年市场行情得知，从二月一日起的300天内，西红杮市场售价与上市时间的关系用图①的一条折线表示；西红杮的种植成本与上市时间的关系用图②的抛物线段表示.（1）写出图①表示的市场售价与时间的函数关系式P=f（t）；写出图②表示的种植成本与时间的函数关系式Q=g（t）；（2）认定市场售价减去种植成本为纯收益，问何时上市的西红杮收益最大？（注：市场售价和种植成本的单位：元/102 kg，时间单位：天）