Question

____ nearly all behavior is learned behavior is a basic assumption of social scientists.

A．/

B．That

C．It is acceptable

D．When

Answer 1

B 

根据句子的结构分析，句中的nearly all behavior is learned behavior是一个完整的句子在充当主语，称为主语从句。that引导主语从句只起连接作用，没有实际含义，但不能省略。