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

Example Input: Sentence: 'a tower type building structure with a large clock and many windows in front of a cloudy blue sky'. Replace the letter 'n' with 'x' in the sentence.
Example Output: a tower type buildixg structure with a large clock axd maxy wixdows ix froxt of a cloudy blue sky

Example Input: Sentence: 'two children who are standing next to a white fire hydrant'. Replace the letter 't' with 'r' in the sentence.
Example Output: rwo children who are sranding nexr ro a whire fire hydranr

Example Input: Sentence: 'a group of animals stand around in the mud'. Replace the letter 'l' with 'r' in the sentence.
Example Output:
a group of animars stand around in the mud