TASK DEFINITION: In this task, you need to replace a letter in the sentence with another given letter.
PROBLEM: Sentence: 'a blue and white train is coming down some tracks'. Replace the letter 'b' with 'u' in the sentence.

SOLUTION: a ulue and white train is coming down some tracks

PROBLEM: Sentence: 'a no parking sign next to a car riding down a street'. Replace the letter 'g' with 'l' in the sentence.

SOLUTION: a no parkinl siln next to a car ridinl down a street

PROBLEM: Sentence: 'a man swings a tennis racket as a tennis ball flies toward him'. Replace the letter 'm' with 'u' in the sentence.

SOLUTION:
a uan swings a tennis racket as a tennis ball flies toward hiu