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

Example Input: Sentence: 'a couch, footrest, tv and other furniture are arranged in a living room'. Replace the letter 'o' with 'g' in the sentence.
Example Output: a cguch, fggtrest, tv and gther furniture are arranged in a living rggm

Example Input: Sentence: 'a gray elephant standing next to green bushes'. Replace the letter 'e' with 'o' in the sentence.
Example Output: a gray olophant standing noxt to groon bushos

Example Input: Sentence: 'a couple of elephants that are drinking some water'. Replace the letter 'u' with 'l' in the sentence.
Example Output:
a colple of elephants that are drinking some water