王士祯《四部稿》中记载：“大抵徽商……其所积蓄，则十一在内，十九在外。”材料反映了徽商（   ）

如图，∠ACB=90°，AC=3，BC=4，则以AB为边长的正方形面积为____ 

进行基因筛检有助于发现某些早期癌症，但也会带来一些负面效应。这些负面效应是（  ）

  The students were having their chemistry（化学）class. Miss Li was telling the children what water was like. After that, she asked her students, “What's water?" No one spoke for a few minutes．Miss Li asked again，“Why don't you answer my question？Didn't I tell you what water is like？”
Just then a boy put up his hand and said，"Miss Li，you told us that water has no color and no smell．But where to find such kind of water？The water in the river behind my house is always black and it has a bad smell．"Most of the children agreed With him．
“I'm sorry，children．”said the teacher，"Our water is getting dirtier and dirtier．That's a problem”．