．The fact has worried many scientists the earth is becoming warmer and warmer these years

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A. what
B. which
(答案→)C. that
D. though
解析：考查同位语从句。句意；地球这些年以来正在变得越来越暖和，这个事实已经使很多科学家忧心忡忡。主句是The fact has worried many scientists，而后面的从句为同位语从句，修饰主句主语the fact，补充解释它（即该事实）的具体内容。从句中不缺少句子成分，故引导词用that。选C。