[单选题] 天然气为无色无味的易燃气体,其83%~99%的成分为()。天然气液态相对密度(水=1)约为0.45,由液态变为气态体积扩大600倍,爆炸极限为5%~14%。遇火源、热源有着火爆炸危险,与氯气、次氯酸、液氧等强氧化剂接触剧烈反应。吸入高浓度的天然气能造成人窒息死亡。( ) A. 甲烷 B. 乙烷 C. 丙烷 D. 丁烷
第16题: [单项选择]A. I often write to you. B. I Write some letters. C. Once a month. D. I often go to see my parents. 参考答案:C 答案解析:[解析] How often do you write to your parents