全球变暖是我们目前面临的一个大问题，不过全世界都过分关注二氧化碳，却忽略了另外一个重要的气体——甲烷。 Fred Krupp: Let's launch a satellite to track a threatening greenhouse gas 我们能否发射一颗卫星来追踪威胁地球的温室气体？ We've got a big problem on our hands with global
名人演讲特辑之四：道格拉斯“七月四日对美国黑奴意味着什么” The Meaning of July Fourth for the Negro By Frederick Douglas Fellow Citizens, I am not wanting in respect for the fathers of this republic. The signers of the Declaratio
Hi, everybody. This week, we continued our mission to destroy ISIL. This remains a difficult fight, and the situation in Syria and Iraq is incredibly complex. ISIL is entrenched, including in urban ar
