When he was alive, the old scientist used to say that knowledge ＿＿from practice and he gained his experience by doing a lot of practical work.

A．was coming

B．had come

C．comes

D．would come

行为主义心理学是关于行为的性质和行为改变过程的理论，创立于20世纪初期，被认为是继精神分析理论之后心理学史上的第一思潮。