fashions differ from country to country may reflect the culture difference from one aspect

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A. What
(答案→)B. That
C. This
D. Which
解析：what在引导的主语从句、宾语从句、表语从句中充当句子成分，而that在引导的上述从句中不充当句子成分，只起连接作用。that引导的主语从句常可用it充当形式主语。例如：It is wellknown that Taiwan is part of China. （众所周知，台湾是中国领土不可分割的一部分。）