这个英语句子中为什么to后面加动词ing?

问题描述:

这个英语句子中为什么to后面加动词ing?
Accustomed though we are to speaking of the films made before 1927 as “silent”,the film has never been,in the full sense of the word, silent.

这个倒装.真少见.正常的Accustomed 在to 前面
意思是习惯于,to 为介词