题目

能使带火星木条复燃的气体是（ ）           A. 空气                                  B. 氧气                                  C. 氮气                                  D. 二氧化碳 答案：B—What were you doing at this time yesterday?—I _______ with my friends .A. am chatting B. was chatting C. chatted B 【解析】句意：——昨天这个时候你在做什么？——我在和我朋友聊天。根据第一句可知是过去进行时态；故选B