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

Example Input: Sentence: 'a dog laying in front of a horses stall with the horse peeking over the half door'. Replace the letter 'a' with 'b' in the sentence.
Example Output: b dog lbying in front of b horses stbll with the horse peeking over the hblf door

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 church building has a tall clock tower'. Replace the letter 'h' with 'a' in the sentence.
Example Output:
a caurca building aas a tall clock tower