"Cut down"是一个及物动词短语，意思是 "砍倒"，即将树木或其他物体砍倒。

一般情况下中间不需要加任何东西。例如:- The lumberjack cut down the tree.- The city decided to cut down the old buildings to make room for new development.不过如果是像 "cut down on something"的短语，意思是"减少某物的消耗"，那么中间需要加一个 "on"。例如：- I'm trying to cut down on my sugar intake.- He needs to cut down on smoking if he wants to stay healthy.