请问,be used to doing是习惯于,可在这句里为什么是to make?

题目

请问,be used to doing是习惯于,可在这句里为什么是to make?
The wood is used to make desks and chairs

答案

The wood is used to make desks and chairs
这个是被动句
木头被用来做桌子和凳子