TASK DEFINITION: In this task, you need to replace a letter in the sentence with another given letter.
PROBLEM: Sentence: 'a open entrance leading to a set of closed doors'. Replace the letter 'd' with 'f' in the sentence.

SOLUTION: a open entrance leafing to a set of closef foors

PROBLEM: Sentence: 'adult man on grassy field playing disc game'. Replace the letter 'n' with 'l' in the sentence.

SOLUTION: adult mal ol grassy field playilg disc game

PROBLEM: Sentence: 'a crowd of people are waiting in line for food'. Replace the letter 'f' with 'm' in the sentence.

SOLUTION:
a crowd om people are waiting in line mor mood