Many people believe we are heading for environmental disaster _____ we radically change the way we live.
A. but
B. although
C. unless
D. lest
此题考查连词。句意:很多人认为如果我们不彻底改变生活方式,我们将面临环境灾难。unless相当于if not,表示“如果不……将……”,除非,符合句意,故选C。
考点:词汇