（6分）H2、CO、和CH4都是初中化学常见的气体。 （1）可燃性气体与空气混合

Since every coin has two sides, living in large modern cities offers us many advantages, meanwhile, causes many troubles. Better education and better jobs are easy to get, and better medical care is convenient to receive in large modern cities.
People are usually well informed due to the advanced media, such as television, newspaper and net PC. Large modern cities also provide various night-life activities for the city-dwellers(城市居民). The public places like cinema, bar, disco-ball are everywhere.
On the other hand, large modern cities are too big to control, so the traffic jams and traffic accidents often happen, and the social security is a headache problem. And city-dwellers have to face the housing problem. Usually a house is too expensive for the salary earning class to buy and the rent is also high. Moreover, noise and pollution in large cities bring harm to people’s health.
Living in large modern cities

Advantages	● It’s easy to get better education, better jobs and 53._________. ● People are usually 54.______________ because of the advanced media. ● People can have various night-life activities in modern cities.
55.___________	● The society is not 56. ___________. ● Citizens have to face the housing problem. ● Noise and pollution in large cities 57. __________ people’s health.