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

Example Input: Sentence: 'a couple of people that are petting a horse'. Replace the letter 'e' with 'p' in the sentence.
Example Output: a couplp of ppoplp that arp pptting a horsp

Example Input: Sentence: 'a man is ordering food from a mobile food truck'. Replace the letter 'r' with 'q' in the sentence.
Example Output: a man is oqdeqing food fqom a mobile food tquck

Example Input: Sentence: 'this is a bird sitting in some grass'. Replace the letter 's' with 'l' in the sentence.
Example Output:
thil il a bird litting in lome grall