人为原因:人多地少,过垦放牧,修路、采矿等活动破坏。
已知若x,y满足约束条件x≥-1y≥x3x+2y≤5,则z=y﹣13x的最小值为____
Sam has got a bike. He goes to school by bike. Amy hasn't got a bike. Her father has got a car. She goes to school in her father's car. Daming hasn't got a bike. He goes to school by bus.