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

Example Input: Sentence: 'a horse in a country field with woods in the background'. Replace the letter 'a' with 'i' in the sentence.
Example Output: i horse in i country field with woods in the bickground

Example Input: Sentence: 'young boy leaping into air with tennis racket with dog below him'. Replace the letter 't' with 'r' in the sentence.
Example Output: young boy leaping inro air wirh rennis racker wirh dog below him

Example Input: Sentence: 'a gray and white dog sitting on a white mattress'. Replace the letter 'n' with 'y' in the sentence.
Example Output:
a gray ayd white dog sittiyg oy a white mattress