、The virtues of thrift（节俭）and hard work is vital for everyone, is often the case in any society.
A. as
B. that
C. when
D. where
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(答案→)A. as
B. that
C. when
D. where
解析：考察非限制性定语从句。本题中的关系代词as指代前面一句话的内容，在句中做主语。As is often the case这是常有的事情。句意：在很多社会里这是常有的事情，节俭和努力对每个人都很重要。That不能引导非限制性定语从句，where和when只能在句中做状语。故A正确。