兰州市政府正在加大对空气污染的治理力度。造成兰州市城区空气污染的原因主要有 ①工厂污水；②汽车尾气；③工厂废气；④施工、环卫造成的二次扬尘；⑤固体垃圾

张赛群《中国近现代“国进民退”现象分析》认为，近现代以来，中国曾出现过几次明显的“国进民退”现象。一是洋务运动时期在“自强”名义下进行的一系列政府经营；二是20世纪三四十年代在战争环境下蒋介石政府的统制经济；三是建国初期为实现公有制而进行的“三大改造”……而第三次也是最彻底的国进民退。作者认为“三大改造”导致国进民退的理由是（    ）

D

    On April 26, China's first homemade aircraft carrier(航空母舰) hit the water in Dalian, Liaoning. It is China's second aircraft carrier and it has no name yet. It was designed in China.

    It is about 315 meters long and 75 meters wide. It is a bit larger than three soccer fields. It can carry 40 to 50 planes.It is the largest and best ship China has ever built.

    An aircraft carrier is like an airport on the sea. It can carry hundreds of planes. Planes fly from and land back on it, and soldiers work and live on it. It is expensive to build an aircraft carrier. It costs a lot of money and uses a lot of steel. It also uses technologies. Finally, it takes years to build.

    Today, not many countries own an aircraft carrier or have the ability to build one. When the new carrier is finished, China will become the seventh country in the world that can build an aircraft carrier by itself, after the US, Russia, UK, France, Italy and Spain.