TASK DEFINITION: In this task, you need to replace a letter in the sentence with another given letter.
PROBLEM: Sentence: 'a small train is on the tracks by a house'. Replace the letter 'l' with 'x' in the sentence.

SOLUTION: a smaxx train is on the tracks by a house

PROBLEM: Sentence: 'a giraffe and a zebra stare at each other'. Replace the letter 'g' with 'l' in the sentence.

SOLUTION: a liraffe and a zebra stare at each other

PROBLEM: Sentence: 'zebras sitting in an area with rocks in the background'. Replace the letter 's' with 'c' in the sentence.

SOLUTION:
zebrac citting in an area with rockc in the background