The correct answer is 'by.' Key Points - Let us look at the usage of the given options: - We use in for something inside or enclosed by something else. Example: We live in the city. - We use of when we want to show that people or things relate to other things or people. Example: Tiffany stared at the floor of her room. - We use by meaning 'not later than' to refer to arrangements and deadlines. Example: The postman is always here by 11 am. - We can use 'with' when you're talking about people, or things being together. Example: I was with Jane yesterday when the accident happened. - Correct sentence: He succeeded by dint of perseverance and hard work.