In this task, you need to replace a letter in the sentence with another given letter.

Example Input: Sentence: 'a box of a dozen doughnuts all varieties'. Replace the letter 'l' with 'i' in the sentence.
Example Output: a box of a dozen doughnuts aii varieties

Example Input: Sentence: 'a man who is surfing in a wave in the ocean'. Replace the letter 'a' with 'u' in the sentence.
Example Output: u mun who is surfing in u wuve in the oceun

Example Input: Sentence: 'a goat follows a dog in a field'. Replace the letter 'i' with 'z' in the sentence.
Example Output:
a goat follows a dog zn a fzeld