A. 瓦斯的开发和利用 B. 煤炭安全的最大威胁 C. 瓦斯的“变废为宝” D. 从“夺命杀手”到战略资源
A. 不解之谜 B. 无因之果 C. 千古之谜 D. 千古之奇
A. 活跃 B. 频繁 C. 厉害 D. 严重
A. 正确 B. 错误
A. Giving up hope means giving up happiness. B. Letting go of hope is at times a better choice. C. Hope is what makes people move on. D. Hope frequently gets in the way of happiness.