题目

 _______, a learned man makes fewer mistakes in life than a man without knowledge. A. In general            B. As general   C. On general         D. At general 答案：A设x，y满足约束条件，若目标函数z=ax+by（a＞0，b＞0）的值是最大值为12，则的最小值为（ ）A．B．C．D．4