题目

造成大气污染的SO2主要来源于A．自然界硫化物分解          B．火山喷发C．汽车排出的废气            D．大量含硫燃料燃烧  答案：D解析: — How are you doing all these years, Jim?   — Nothing new. Everything is going on ____it was years ago.   [     ]A. as           B. while                 C. when          D. since