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

Example Input: Sentence: 'a group of sheep is standing in a grassy field'. Replace the letter 'g' with 'p' in the sentence.
Example Output: a proup of sheep is standinp in a prassy field

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 boy in a red shirt holding a teddy bear in a chair'. Replace the letter 'a' with 'h' in the sentence.
Example Output:
h boy in h red shirt holding h teddy behr in h chhir