Detailed Instructions: In this task, you need to replace a letter in the sentence with another given letter.
Problem:Sentence: 'a young boy riding skis across a snow covered slope'. Replace the letter 'y' with 'u' in the sentence.
Solution:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
a uoung bou riding skis across a snow covered slope