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

Example Input: Sentence: 'people wait for a train on a snowy sidewalk'. Replace the letter 'n' with 'm' in the sentence.
Example Output: people wait for a traim om a smowy sidewalk

Example Input: Sentence: 'a large elephant standing outside beside a tree'. Replace the letter 'e' with 'y' in the sentence.
Example Output: a largy ylyphant standing outsidy bysidy a tryy

Example Input: Sentence: 'two men in a large emergency vehicle on a city street'. Replace the letter 'i' with 'p' in the sentence.
Example Output:
two men pn a large emergency vehpcle on a cpty street