我市的“燃气改造工程正在迅速推进．

（1）已知燃气的热值为4×l0⁷J/m³，燃气的密度为1.2kg/m³，求完全燃烧多少千克燃气可放出8.4×l0⁵J的热量．

（2）如果这些热量全部被水吸收，则可以使质量为2.5kg初温为15℃的水温度升高到多少摄氏度？

（3）将加热后的水（假设质量不变）倒入暖水瓶中放在水平桌面上，若暖水瓶与桌面的接触面积为70cm²，此时暖水瓶对桌面的压强为5×10³pa．求暖水瓶的质量．

用同样长的小棒摆成1个四边形，最少用（   ）根

——I'm going to Hainan on vacation next week.

——___________.

    Some people have very good memories and can easily learn quite long poem（诗歌）by heart. Some people have1memories and can only2things that they have said again and again.
    The3English writer Charles Dickens said that he could walk down 4 street in London and then tell you the name of every shop on5sides of the street. Great men in the world have wonderful memories.
    A good memory is a great help in learning a language. Everybody learns 6language by remembering what he hears7he is a small child. Some children live with their parents in foreign countries and they seem8two languages as9as one. In school it is not so easy to learn foreign languages10students have little time11 it and they are busy with other subjects as well.
    A man's mind is quite like a camera but it12photos of what we see and it can also take photos of what we feel, hear, smell and taste. When we take a real photo13a camera there is much work14before the photo is finished and ready to show to our friends.15 the same way there is much work to do before we can keep a picture forever in our mind.