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

Example Input: Sentence: 'a woman is standing on a street curb'. Replace the letter 'a' with 't' in the sentence.
Example Output: t womtn is sttnding on t street curb

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: 'a fire hydrant is covered with graffiti and spray paint as it stands in front of colorful building in the background'. Replace the letter 'i' with 'g' in the sentence.
Example Output:
a fgre hydrant gs covered wgth graffgtg and spray pagnt as gt stands gn front of colorful bugldgng gn the background