题目

Today, roller skating is easy and fun. But a long time ago, it wasn't easy at all. Before 1750, the idea of skating didn't exist. That changed because of a man named Joseph Merlin. Merlin's work was making musical instruments. In his spare time he liked to play the violin. Joseph Merlin was a man of ideas and dreams. People called him a dreamer. One day Merlin received an invitation to attend a fancy dress ball. He was very pleased and a little excited. As the day of the party came near, Merlin began to think how to make a grand entrance at the party. He had an idea. He thought he would get a．西气东输工程的主要意义在于（    ） A. 改变用气地区能源构成，改善大气环境   B. 降低散热量，减轻城市的热岛效应 C. 减少气源地天然气对大气的污染         D. 改变天然气化学工业过分集中的现状