Instructions: 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.
Input: Sentence: A shopping cart rolls by itself across a parking lot. Then it gets to a field. The cart rolls only a little more after it enters the field. Question: Why does this happen? (A) the parking lot is a rougher surface (B) the field is a rougher surface
Output:
the field is a rougher surface