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

Example Input: Sentence: 'a bunch of giraffe stand around on a dirt covered area'. Replace the letter 'e' with 'p' in the sentence.
Example Output: a bunch of giraffp stand around on a dirt covprpd arpa

Example Input: Sentence: 'a polar bear relaxing in a man-made pool'. Replace the letter 'r' with 'x' in the sentence.
Example Output: a polax beax xelaxing in a man-made pool

Example Input: Sentence: 'a clear vase with several pretty yellow and red petaled flowers'. Replace the letter 'y' with 'k' in the sentence.
Example Output:
a clear vase with several prettk kellow and red petaled flowers