题目

    Last month, Justin Valdez, a college student, was shot in a subway station in San Francisco. The surveillance video(监控录像) showed that before Justin was killed, the killer pulled out his gun several times, and even wiped his nose with it. However, nobody noticed the killer. The surrounding passengers all focused on their cell phones.     We may see the same scene everywhere in our life: in subway stations, restaurants, elevators and so on, people are watching their cell phones. From a family reunion  to a date with a friend, people couldn’t stop checking their twitteQQ是一款流行的互联网即时通讯（聊天）工具，现在很多中小学生进行QQ升级，如图，据资料表明要想升级得到一个“月亮”，需在线140小时，若使用的电脑平均功率是200w，那么：（1）1个QQ用户使用一台电脑升级一个“月亮”消耗多少电能？（2）追求虚拟的等级而开机让QQ在线，会造成大量的电能浪费．如果这些消耗的电能全部用来烧水，可以将多少千克20℃的水加热到100℃？（3）若这些水用煤气加热，在加热过程中，煤气放出的热量只有50%被水吸收，则需完全燃烧多少立方米煤气？（煤气的热值是4.0×107J/m3）