cut down
一般指的是实物
例：
1.削减
He tried to cut down on smoking but failed.
他试图少抽烟,但没成功.
2.缩短
Cut down the article so as to make it fit the space available on the paper.
把文章缩短一些,这样就能排进报纸有限的版面中.
3.砍倒
reduce
多指数量的减少