instruction:
In this task, you need to replace a letter in the sentence with another given letter.
question:
Sentence: 'a crooked street sign on a damaged sidewalk'. Replace the letter 'm' with 'u' in the sentence.
answer:
a crooked street sign on a dauaged sidewalk


question:
Sentence: 'a boy riding his skate board on an obstacle course'. Replace the letter 'e' with 'b' in the sentence.
answer:
a boy riding his skatb board on an obstaclb coursb


question:
Sentence: 'a yellow and black train entering a train station'. Replace the letter 'e' with 'u' in the sentence.
answer:

a yullow and black train unturing a train station