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

Example Input: Sentence: 'a zebra standing by a pile of large rocks'. Replace the letter 'i' with 'x' in the sentence.
Example Output: a zebra standxng by a pxle of large rocks

Example Input: Sentence: 'a man walking a horse on a dirt track'. Replace the letter 't' with 's' in the sentence.
Example Output: a man walking a horse on a dirs srack

Example Input: Sentence: 'a man and woman ride horses through hilly terrain'. Replace the letter 'o' with 'i' in the sentence.
Example Output:
a man and wiman ride hirses thriugh hilly terrain