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

Example Input: Sentence: 'a brown door  that says gentlemen and a toilet'. Replace the letter 'o' with 'f' in the sentence.
Example Output: a brfwn dffr  that says gentlemen and a tfilet

Example Input: Sentence: 'a couple of brown bears walking across a lush green field'. Replace the letter 'w' with 'o' in the sentence.
Example Output: a couple of broon bears oalking across a lush green field

Example Input: Sentence: 'a boy holding an umbrella standing on a street'. Replace the letter 'e' with 'p' in the sentence.
Example Output:
a boy holding an umbrplla standing on a strppt