科学家将人胰岛素基因转入大肠杆菌内，利用细菌合成人胰岛素，下列叙述正确的是（   ）

①运用组织培养技术②细菌的变异是可遗传的③运用转基因技术④说明基因在染色体上．

凡是说话做事符合道德要求的，就会获得好名誉；反之，说话做事违反了道德要求，就会损害自己的名誉。（   ）

Dear Wang Tao,

    I'm so glad to read about the changes taking place in your city. I am happy that you can travel by subway in Chongqing, though there are only six lines there. Here is London we have twelve lines.

    The London Underground is very famous. It's famous for several reasons. Firstly, part of the underground railway today is the oldest in the world. It opened in 1863. Secondly, the London Underground is also the first line to have electric（电动的）trains in 1890. Thirdly, the London Underground is the second largest metro（地下铁道）system in the world, after the Shanghai Metro. There are 270 stations in the Underground and it has 402 kilometers of tracks (轨道). What's more, the city of London itself helps make the transportation（交通）system famous! I've got a few photos to help you build a clear picture of the Underground in my city. They are together with this mail.

    In your e-mail, you also said workers were building more lines. I'm sure your city is developing fast. Maybe you can send me a few photos of your city today. I really want to see the changes taking place there. I'm happy for you to live in an ancient city with such a new look!

    So much for now. I'll write soon again. Best wishes!

Yours,John

以直角三角形的三边为边长分别向外作正方形，已知其中两个正方形的面积分别为20和16，则第三个正方形的边长为（       ）