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

Example Input: Sentence: 'a couple of white street signs sitting on top of a pole'. Replace the letter 'n' with 't' in the sentence.
Example Output: a couple of white street sigts sittitg ot top of a pole

Example Input: Sentence: 'giraffes behind a fence in the trees'. Replace the letter 'h' with 'l' in the sentence.
Example Output: giraffes belind a fence in tle trees

Example Input: Sentence: 'street scene with a bus going through a green light'. Replace the letter 'i' with 'e' in the sentence.
Example Output:
street scene weth a bus goeng through a green leght