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

Example Input: Sentence: 'subway train approaching the platform of a subway station'. Replace the letter 'y' with 'c' in the sentence.
Example Output: subwac train approaching the platform of a subwac station

Example Input: Sentence: 'a man in a baseball cap watching something in the air'. Replace the letter 'g' with 'o' in the sentence.
Example Output: a man in a baseball cap watchino somethino in the air

Example Input: Sentence: 'an athlete is performing on a playing field'. Replace the letter 'a' with 'q' in the sentence.
Example Output:
qn qthlete is performing on q plqying field