TASK DEFINITION: In this task, you need to replace a letter in the sentence with another given letter.
PROBLEM: Sentence: 'a sign sitting on the side of a snow covered slope'. Replace the letter 'e' with 'g' in the sentence.

SOLUTION: a sign sitting on thg sidg of a snow covgrgd slopg

PROBLEM: Sentence: 'a person flying a kite on the beach  between some trees'. Replace the letter 's' with 'k' in the sentence.

SOLUTION: a perkon flying a kite on the beach  between kome treek

PROBLEM: Sentence: 'three mountain goats on a rock with grass around it'. Replace the letter 'g' with 'b' in the sentence.

SOLUTION:
three mountain boats on a rock with brass around it