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

Example Input: Sentence: 'horses drink and graze the field and water'. Replace the letter 'i' with 'c' in the sentence.
Example Output: horses drcnk and graze the fceld and water

Example Input: Sentence: 'a couple sits on a bench in the countryside'. Replace the letter 'y' with 'k' in the sentence.
Example Output: a couple sits on a bench in the countrkside

Example Input: Sentence: 'a young girl on a spring board in a playground'. Replace the letter 'p' with 'o' in the sentence.
Example Output:
a young girl on a soring board in a olayground