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

Example Input: Sentence: 'a horse in a country field with woods in the background'. Replace the letter 'a' with 'i' in the sentence.
Example Output: i horse in i country field with woods in the bickground

Example Input: Sentence: 'a back pack and lap top sit on the kitchen counter'. Replace the letter 't' with 'k' in the sentence.
Example Output: a back pack and lap kop sik on khe kikchen counker

Example Input: Sentence: 'a cow and calf stand together in a field'. Replace the letter 'e' with 'w' in the sentence.
Example Output:
a cow and calf stand togwthwr in a fiwld