nearly all behavior is learned behavior is a basic assumption has been put forward by the social scientists.
A. What, that
B. That, what
C. What, what
D. That, that
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A. What, that
B. That, what
C. What, what
(答案→)D. That, that
解析：考查名词从句的引导词。第一空that引导的是一个主语从句,that在句中不充当任何成分，只起连接作用。第二空that引导同位语从句，对名词a basic assumption进行补充说明。That同样在句中不充当任何成分，只起连接的作用。故D正确。