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

Example Input: Sentence: 'a cat is watching a computer with a video of a cat'. Replace the letter 't' with 'a' in the sentence.
Example Output: a caa is waaching a compuaer wiah a video of a caa

Example Input: Sentence: 'a group of men sitting at a desk with lap top computers'. Replace the letter 'p' with 'z' in the sentence.
Example Output: a grouz of men sitting at a desk with laz toz comzuters

Example Input: Sentence: 'a crowd of people on a sandy beach flying kites'. Replace the letter 'a' with 'g' in the sentence.
Example Output:
g crowd of people on g sgndy begch flying kites