The only system I know will help you remember what you have heard at a lecture is the sys

问题补充：

The only system I know will help you remember what you have heard at a lecture is the system of keeping notes.

A. what

B. that

C. where

D. one

答案：

A. what

(答案→)B. that

C. where

D. one

解析：句意：我知道的记住在课堂上所学内容的唯一方法就是记笔记。这个句子包含一个定语从句，关系词在从句中作主语，指物，故用that，选B。