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

Example Input: Sentence: 'a boy taking a nap with his dog on a bed'. Replace the letter 'o' with 'i' in the sentence.
Example Output: a biy taking a nap with his dig in a bed

Example Input: Sentence: 'a crowd stands under a set of lights in the ceiling and one person holds up a cell phone'. Replace the letter 'r' with 'f' in the sentence.
Example Output: a cfowd stands undef a set of lights in the ceiling and one pefson holds up a cell phone

Example Input: Sentence: 'a black cat laying down in a bathroom sink'. Replace the letter 'a' with 't' in the sentence.
Example Output:
t bltck ctt ltying down in t btthroom sink