TASK DEFINITION: In this task, you need to replace a letter in the sentence with another given letter.
PROBLEM: Sentence: 'a crowd stands under a set of lights in the ceiling and one person holds up a cell phone'. Replace the letter 'r' with 'f' in the sentence.

SOLUTION: a cfowd stands undef a set of lights in the ceiling and one pefson holds up a cell phone

PROBLEM: Sentence: 'horses drink and graze the field and water'. Replace the letter 'i' with 'c' in the sentence.

SOLUTION: horses drcnk and graze the fceld and water

PROBLEM: Sentence: 'a group of young guys riding a skateboard across a bridge'. Replace the letter 'n' with 'g' in the sentence.

SOLUTION:
a group of yougg guys ridigg a skateboard across a bridge