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

Example Input: Sentence: 'a man is standing on a snowboard, atop a mountain'. Replace the letter 'd' with 'u' in the sentence.
Example Output: a man is stanuing on a snowboaru, atop a mountain

Example Input: Sentence: 'a group of small children sitting at a table in front of a pizza'. Replace the letter 'r' with 'd' in the sentence.
Example Output: a gdoup of small childden sitting at a table in fdont of a pizza

Example Input: Sentence: 'a close up of a bird near a laying giraffe'. Replace the letter 'a' with 'u' in the sentence.
Example Output:
u close up of u bird neur u luying giruffe