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

Ex Input:
Sentence: 'a mobile phone and a set of keys on a key chain'. Replace the letter 's' with 'j' in the sentence.

Ex Output:
a mobile phone and a jet of keyj on a key chain

Ex Input:
Sentence: 'a small bird perched on some thin branches'. Replace the letter 'a' with 'f' in the sentence.

Ex Output:
f smfll bird perched on some thin brfnches

Ex Input:
Sentence: 'darkness surrounding an unidentified object with bright colors'. Replace the letter 'o' with 'k' in the sentence.

Ex Output:
darkness surrkunding an unidentified kbject with bright cklkrs