A:①②
B:①③
C:②④
D:③④
Only when we realize how serious the environment is damaged, _______ is usually ignored, ______ try our best to fight against it.
求下面各组数的最大公因数.
18和24____
48和72____
56和84____
维护未成年人合法权益最正规、最权威、最有效的手段是向政府有关部门反映情况,寻求帮助。( )
东北地区甜菜集中分布在____平原和松嫩平原。