You are given a sentence, a question and two answer options ('A' and 'B'). Your task is to find the correct answer (return the string of the correct option, not 'A' or 'B') for the given question.
Q: Sentence: A matchbox can slide across a greenhouse floor, but it doesn't move as fast as when it is slid across the backyard. Question: Which surface is the smoother one? (A) greenhouse floor (B) backyard
A: 
greenhouse floor