It was not until then that I came to know that knowledge ____only from practice

题目

It was not until then that I came to know that knowledge ____only from practice
A.had come B has come C came D comes
请问It was not until 最好能翻译下句意思
我觉得应该是现在完成时或是过去完成时,可为什么是D
麻烦分析下ABC不能用的原因

答案

直到那时才.
我直到那时才逐渐认识到,知识只能来源于实践.
照理说,从句的时态要根据主句来定,但涉及到一些真理、规律性的除外.像这句话,知识来源于实践,是规律性的结论,这都要用一般时态的,所以选comes.
明白?