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

Example Input: Sentence: 'a person with a cell phone standing next to a train'. Replace the letter 's' with 't' in the sentence.
Example Output: a perton with a cell phone ttanding next to a train

Example Input: Sentence: 'a person under an open umbrella in the sand'. Replace the letter 'd' with 'h' in the sentence.
Example Output: a person unher an open umbrella in the sanh

Example Input: Sentence: 'a bicycle decorated with flowers, chained to a stop sign'. Replace the letter 'e' with 'q' in the sentence.
Example Output:
a bicyclq dqcoratqd with flowqrs, chainqd to a stop sign