由A(2,3),B(﹣3,﹣7),
得 {2k+b=3
我国四大地理区域中农作物一年一熟或两年三熟的地区是____地区;我国机械化程度最高、提供商品粮最多的粮食基地是____平原。
We should try to solve the food safety. It is a serious _______ in our country.