关于甲大洲的叙述，正确的是（  ）

近年来儿童性早熟现象日益突出，如男孩早早长出胡须、女孩月经提早等，这与摄入含激素类物质有密切关系，这些物质最有可能含有的激素是(     )

读短文并按要求完成相应任务
    Today was the first day of the summer holiday．My friends and I went out together．We went swimming in the swimming pool．We swam for an hour．I did not swim well，but I enjoyed it very much．We had lunch in a fast—food restaurant．I had a sandwich and some orange juice．Alice had a hamburger．Jack had a lot of French fries and some cola．We went shopping in a supermarket．I bought a pink dress．Alice bought a pretty hat．Jack did not buy anything．
    We went home at 3 o'clock in the afternoon．We 、were tired，but we were happy．

下列说法，正确的是（   ）

已知m+n=3，m﹣n=2，则m²﹣n²=____．