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

Example Input: Sentence: 'a man on the news, watched on the television'. Replace the letter 'o' with 'z' in the sentence.
Example Output: a man zn the news, watched zn the televisizn

Example Input: Sentence: 'a red stop sign sitting on the side of a road'. Replace the letter 'r' with 'o' in the sentence.
Example Output: a oed stop sign sitting on the side of a ooad

Example Input: Sentence: 'three white sheep walking down a town road'. Replace the letter 'n' with 'z' in the sentence.
Example Output:
three white sheep walkizg dowz a towz road