题目

如图，△ABC的中线AD，BE相交于点F．若△ABF的面积是7，则四边形CEFD的面积是____． 答案：【答案】7【解析】根据等底等高的三角形的面积相等可知三角形的中线把三角形分成面积相等的两个三角形，然后表示出S△ABE=S△ACD=S△ABC，再表示出S△ABF与S四边形CEFD，即可得解．∵AD、BE是△ABC的中线，∴S△ABE=S△ACD=S△ABC，∵S△ABF=S△ABE-S△AEF，S四边形CEFD=S△ACD-S△AEF，∴S△ABF=S四边形CEFD=7，故答After spending years searching for a planet with life, scientists may have found one. In September 2010, a team of US scientists discovered an Earth-sized planet called Gliese 581g. It has a surface temperature neither too hot nor too cold for liquid（液态）water. Scientists think there is a chance that the planet could have life.The planet Gliese 581g goes around a star called Gliese 581, which is about 20 light-years from Earth. That is about 194 trillion（万亿）kilometres －500 million times farther away from us than the moon.A spacecraft traveling at a one-tenth of the speed of light would reach Gliese 581g within about 220 years. A human can’t live that long, but robotic explorers could make the job easier. However, our fastest spacecraft don’t come anywhere near that one-tenth light-speed mark.At present, scientists don’t know what the surface might be like on Gliese 581g. What they know is that the planet is at the sight distance from its star to have liquid water. It’s also at the right distance to have an atmosphere that could protect the water if it is on the surface.Although spacecraft won’t be getting there anytime soon, one way to look for life on Gliese 581g is to turn our radio telescopes（望远镜）towards the planet and search for radiation（放射）. By studying the radiation, scientists would find out about the chemicals（化学物质）around the planet and discover it Gliese 581g has an atmosphere. If it has one, studying the atmosphere would give us a good idea if the planet has life or not. But it’ll probably be many years before we can do this properly.People have been arguing about whether there is alien life on Gliese 581g. Any discussion about alien life is just guessing at this point, according to its discoverers.【小题1】 What did scientists find in September 2010?A．A planet with water. B．A planet similar to the earth.C．A planet without life.D．A planet near the earth.【小题2】According to the article, Gliese 581g ________.A．is at the right distance from its starB．moves around the earthC．is as far away from us as the moonD．can be reached in about 220 years【小题3】 Paragraph 5 is mainly about ______.A．the possibility of living on Gliese 581gB．the kinds of chemicals around Gliese 581gC．the way of looking for life on Gliese 581gD．the aim of studying the radiation on Gliese 581g【小题4】Which of the following is the best title for the passage above?A．Gliese 581g, a Likely Living PlanetB．Gliese 581, a Likely Living PlanetC．Gliese 581g and Its StarD．Gliese 581g and Radiation