题目

China is a_____country____the third world. A.developing,belonging       B.developed,belonging to  C.developing,belonging to    D.developed,belongs to 答案：C设变量x，y满足约束条件：y≥xx+2y≤2x≥-2，则z=x-3y+4的最大值为（　　） A、8B、6C、4D、2