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

Example Input: Sentence: 'a number of people sitting on chairs near each other'. Replace the letter 'c' with 'm' in the sentence.
Example Output: a number of people sitting on mhairs near eamh other

Example Input: Sentence: 'a person is riding a skateboard in a skateboard park'. Replace the letter 'a' with 'o' in the sentence.
Example Output: o person is riding o skoteboord in o skoteboord pork

Example Input: Sentence: 'a surfboard in some grass on a field'. Replace the letter 'a' with 'p' in the sentence.
Example Output:
p surfboprd in some grpss on p field