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

Example Input: Sentence: 'a baseball player holding a baseball bat during a baseball game'. Replace the letter 'a' with 'u' in the sentence.
Example Output: u busebull pluyer holding u busebull but during u busebull gume

Example Input: Sentence: 'a plate topped with waffles, bacon and banana slices'. Replace the letter 'a' with 'k' in the sentence.
Example Output: k plkte topped with wkffles, bkcon knd bknknk slices

Example Input: Sentence: 'a couple of cows that are standing in the grass'. Replace the letter 'a' with 'x' in the sentence.
Example Output:
x couple of cows thxt xre stxnding in the grxss