I can't imagine there ________ be a shortage of water in Yunnan, the southwest of China

where there used to be adequate rain. [    ]

A. could  

B. must

C. might  

D. should

2004月年5 月，天然气伴随着“西气东输”的步伐开始走进了江城芜湖的千家万户，传统燃料也随之被逐步取代．天然气燃烧时可以将______能转化为______能．假如燃烧充分，那么天然气与煤气相比，燃烧时每立方米释放出的热量约相差______J．与传统燃料相比，天然气的优点是______（写出一条即可）．