题目

When will the football game begin? A.At 3:00. B.At 2:30. C.At 2:00. 答案：【答案】B【解析】W: Hurry up. The football game begins at two thirty.M: No hurry. We still have thirty minutes.单项式﹣πr2的系数是（    ），次数是（    ）．