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

Example Input: Sentence: 'a person on a snowboard does an air trick'. Replace the letter 'n' with 'o' in the sentence.
Example Output: a persoo oo a soowboard does ao air trick

Example Input: Sentence: 'four people are playing an interesting game in the park'. Replace the letter 'e' with 'x' in the sentence.
Example Output: four pxoplx arx playing an intxrxsting gamx in thx park

Example Input: Sentence: 'a zebra walks across a field of green grass'. Replace the letter 'a' with 'y' in the sentence.
Example Output:
y zebry wylks ycross y field of green gryss