Scientists are warning that emissions of carbon (碳排放) are cut, we could be heading for an environmental disaster.
A. before
B. as
C. unless
D. in case
网友回答
A. before
B. as
(答案→)C. unless
D. in case
解析：C 考察连词。Before在…之前；as因为，由于；unless除非，如果不；in case万一，假使；句义：科学家警告说如果碳排放不下降，我们会面临环境灾难。根据句义和逻辑关系可知C正确。