TASK DEFINITION: In this task, you need to replace a letter in the sentence with another given letter.
PROBLEM: Sentence: 'a clock mounted above a door entrance with windows'. Replace the letter 's' with 'l' in the sentence.

SOLUTION: a clock mounted above a door entrance with windowl

PROBLEM: Sentence: 'a small bird perched on some thin branches'. Replace the letter 'a' with 'f' in the sentence.

SOLUTION: f smfll bird perched on some thin brfnches

PROBLEM: Sentence: 'subway train approaching the platform of a subway station'. Replace the letter 'y' with 'c' in the sentence.

SOLUTION:
subwac train approaching the platform of a subwac station