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

Example Input: Sentence: 'a group of giraffe standing on top of a dirt field'. Replace the letter 'a' with 'y' in the sentence.
Example Output: y group of giryffe stynding on top of y dirt field

Example Input: Sentence: 'a person jumping up in the air on a snowboard'. Replace the letter 'r' with 'o' in the sentence.
Example Output: a peoson jumping up in the aio on a snowboaod

Example Input: Sentence: 'a woman standing in front of a tent while holding a hairbrush'. Replace the letter 'a' with 't' in the sentence.
Example Output:
t womtn sttnding in front of t tent while holding t htirbrush