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

Example Input: Sentence: 'a skater looks ahead as he rides down a ramp'. Replace the letter 'n' with 'm' in the sentence.
Example Output: a skater looks ahead as he rides dowm a ramp

Example Input: Sentence: 'a kid is sitting on a skateboard outside'. Replace the letter 'd' with 'a' in the sentence.
Example Output: a kia is sitting on a skateboara outsiae

Example Input: Sentence: 'a house cat sits on an oven door, sniffing the oven racks inside'. Replace the letter 'i' with 'y' in the sentence.
Example Output:
a house cat syts on an oven door, snyffyng the oven racks ynsyde