Many people believe we will face environmental disasters we completely change the way we

问题补充：

Many people believe we will face environmental disasters we completely change the way we live.

A. but

B. though

C. unless

D. until

答案：

A. but

B. though

(答案→)C. unless

D. until

解析：but 但是；Though虽然，尽管；unless除非；until直到，常和not一起搭配使用。句意：除非我们改变我们的生活方式，很多人相信我们将要面对生态灾难。故选C。