这个英语句子中为什么to后面加动词ing？

Question

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．

Answer 1

to do是不定式，当to为介词时，后接动词ing形式

Answer 2

这个倒装。。。真少见。正常的Accustomed 在to 前面
意思是习惯于， to 为介词本回答被提问者采纳

Answer 3

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