题目

属于同素异形体的一组物质是（） A . 焦炭和木炭 B . 一氧化碳和二氧化碳 C . 金刚石和石墨 D . 氧气和液氧 答案：C-_        I finish my homework today, Mum?              -No, you _         . You can do it on Saturday.               [     ]A. Must; don't have to                    B. Must; mustn't               C. Can, mustn't                          D. Can; needn't