She often takes n________ by writing down the key words...

根据句意，‘She often takes ______ by writing down the key words in class.’ 这句话意思是‘她常通过在课堂上记下关键词来做……’。在此语境下，‘notes’（笔记）最合适，因为人们通常通过记下关键词来做笔记。