We are accustomed . . . . . . . . doing hard work.

A. in

B. of

C. to

D. with

Answer: Option C

Solution(By Examveda Team)

If you are 'accustomed to' something, you know it so well or have experienced it so often that it seems natural, unsurprising, or easy to deal with. Hence 'to' is the correct preposition to be used.