Fighting an artificial greenhouse effect seems to be the greatest of environmental challenges, ？
A. isn't it
B. does it
C. doesn't it
D. is it
网友回答
A. isn't it
B. does it
(答案→)C. doesn't it
D. is it
解析：C 考察反义疑问句。当反义疑问句的陈述部分是肯定形式的时候，疑问部分使用否定形式，排除BD，根据陈述部分的seems可知doesn’t it符合题意。故C正确。