题目

 ______,there must have been 20000 people there, that is, there are______20000 people there. A. On total; a total of      B. In total; a total ofC. In total; the total of    D. On total; the total of 答案：B（2006•临沂）如图，Rt△ABC中，∠A=90°，AB=4，AC=3，D在BC上运动（不与B、C重合），过D点分别向AB、AC作垂线，垂足分别为E、F，则矩形AEDF的面积的最大值为    ．