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

Example Input: Sentence: 'a zebra is eating hay in a fenced enclosure'. Replace the letter 'e' with 'i' in the sentence.
Example Output: a zibra is iating hay in a fincid inclosuri

Example Input: Sentence: 'a woman sitting on a bench under a gazebo'. Replace the letter 's' with 'u' in the sentence.
Example Output: a woman uitting on a bench under a gazebo

Example Input: Sentence: 'a couple of elephants that are staring at each other'. Replace the letter 'a' with 's' in the sentence.
Example Output:
s couple of elephsnts thst sre stsring st esch other