如图是2002年在北京召开的国际数学家大会的会徽，它由4个相同的直角三角形拼成，已知直角三角形的两条直角边长分别为3和4，则大正方形ABCD和小正方形EFGH的面积比是（　　）

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2015年5月，我国自主三代核电技术“华龙一号”首堆示范工程﹣﹣福清核电站5号机组开工建设，标志着我国核电建设迈进新的时代．下列关于核能发电说法中，正确的是（   ）

阅读短文，完成下列问题

Dear Jenny,

   How are you? I am visiting my cousin Howard in Australia. It is hot in Hong Kong but it is cold in Australia in June. When it is summer in Hong Kong, it is winter in Australia. It is snowing heavily now. I like snow a lot and it is a white world outside. I will play with my cousin in the snow this afternoon. We want to make a snowman. I think it is very interesting!

   I like my cousin's house. It is big and there is a beautiful garden（花园）. We can play ball games. My cousin's neighbors are friendly but they cannot speak Chinese. I talk with them in English.

   See you next month.

 Tony

为除去粗盐中的泥沙、CaCl₂、MgCl₂、Na₂SO₄杂质，得到NaCl，可先将粗盐溶于水，在进行以下操作：①过滤；②加过量的盐酸；③加过量的Na₂CO₃溶液；④加过量的NaOH溶液；⑤加过量的BaCl₂溶液；⑥蒸发．正确的操作顺序是（　　）