义务教育依据法律规定，具有强迫性、免费性、______性。

C

A light emitting diode （发光二极管）, or L．E．D．, is a device that shines when electricity passes through it．But it works differently than traditional kinds of light bulbs．Light emitting diodes use less energy and last much longer than bulbs with a filament （灯丝） inside．L．E．                               D．’s are also cooler to the touch, and shine a lot brighter than they used to．  

Red L．E．D．’s have long been used as signal lights on electronic equipment．But now light emitting diodes also come in blue and other colors．Colored L．E．D．’s are used to show images on everything from wireless phones to huge video signs．And white L．E．D．’s are being used increasingly to replace traditional lighting systems．  

But all these require electricity．In poor countries, people often burn fuel to produce light．But the smoke can make people sick．So an electrical engineering professor from Canada started a project to produce L．E．       D．lighting systems for the developing world．These lights are powered by batteries that can be recharged with energy from the sun．The batteries can also be charged through other ways, such as wind power and water power．

Professor David Irvine-Halliday tells the story of how he got the idea．In 1997, while climbing in the Annapurna mountains in Nepal, he saw a small school．All the children were outside．He looked through a window and saw that inside the school was dark．The school had a sign that read: "We have no teachers．If you want to stay and teach for a few days, we would be very pleased．" Professor Irvine-Halliday says that experience had a big effect on him．Back at the University of Calgary, he was on the Internet one day．He saw a company in Japan selling bright white L．E．                           D．’s．So he built a light with some．This is how he began the Light Up the World Foundation．

48．Compared with traditional kinds of light bulbs, L．E．D．’S________．

A．waste a lot of energy                    B．need shorter time to make

C．shine much brighter                 D．are warmer to touch

49．According to the passage, we know that L．E．D．’s________．

A．will replace all the lights            B．will be more and more popular

C．will be only colored ones               D．will be only used in developing countries

50．According to the passage, we can infer that the purpose of the Light Up the World Foundation is to________．

A．develop L．E．D．lighting system for the developing world                   

B．sell bright white L．E．D．’s

C．collect money for developing countries                                        

D．earn money by selling L．E．D．’s

针对持续陷入僵局的巴以和平进程，国际社会开始新一轮促和努力。联合国安理会2010年4月14日召开会议，专门讨论中东和平问题，与此同时，相关方面围绕如何推动巴以谈判的外交努力也在进行之中。这表明（ ）

A．国际组织在调节国际争端方面都发挥着积极作用

B．联合国在维护世界和平与安全方面发挥着积极作用

C．联合国也有其局限性

D．国际争端都必须在联合国的框架内寻求解决

日本中古文学代表作《源氏物语》产生的时代是（）

A、奈良时期

B、平安时期

C、幕府时期

D、江户时期

患哪些疾病的人员不得从事食品工作？

简述装置凹凸面法兰泄漏的原因。