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

Example Input: Sentence: 'a girl riding a horse is jumping the log'. Replace the letter 'a' with 't' in the sentence.
Example Output: t girl riding t horse is jumping the log

Example Input: Sentence: 'a child holding a tv remote like a phone'. Replace the letter 'i' with 'b' in the sentence.
Example Output: a chbld holdbng a tv remote lbke a phone

Example Input: Sentence: 'a couple of elephants are standing in a grassy field'. Replace the letter 'a' with 'm' in the sentence.
Example Output:
m couple of elephmnts mre stmnding in m grmssy field