In this task, you need to replace a letter in the sentence with another given letter.

Sentence: 'a couple sits on a bench in the countryside'. Replace the letter 'y' with 'k' in the sentence.
a couple sits on a bench in the countrkside

Sentence: 'a guy looking at a tennis ball with a goofy look'. Replace the letter 'a' with 'x' in the sentence.
x guy looking xt x tennis bxll with x goofy look

Sentence: 'people with umbrellas are going down a path in the rain towards a lighthouse'. Replace the letter 'u' with 'y' in the sentence.

people with ymbrellas are going down a path in the rain towards a lighthoyse