Many people believe we will face environmental disasters we pletely change the way we live.
A. but
B. though
C. unless
D. until
网友回答
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。