Helen and Bob are working hard these days because they will put ______ a short play in the school Talent(才艺) show.
由x<y得到ax>ay,则a的取值范围是 ____
下列海域属于我国内海的是( )
我国疆域,许多大江大河源远流长.关于如图中两河说法正确的是( )