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

Example Input: Sentence: 'an elephant in chains converses with a smaller elephant who is not wearing chains'. Replace the letter 'i' with 'm' in the sentence.
Example Output: an elephant mn chamns converses wmth a smaller elephant who ms not wearmng chamns

Example Input: Sentence: 'a busy intersection with cars moving at night'. Replace the letter 's' with 'f' in the sentence.
Example Output: a bufy interfection with carf moving at night

Example Input: Sentence: 'a man and three children standing at a fence watching animals'. Replace the letter 'r' with 'o' in the sentence.
Example Output:
a man and thoee childoen standing at a fence watching animals