题目

The zoo keeper is worried because the number of visitors ________ smaller and smaller. A．become  B．became C．is becoming  D．have become 答案：C 函数y＝－x2＋4x的单调递增区间是 [　　] A．[－2，＋∞) B．[2，＋∞) C．(－∞，－2] D．(－∞，2]