You will be given a definition of a task first, then some input of the task.
You are given a sentence, a question and two answer options ('A' and 'B'). Your task is to find the correct option for the given question. Write down the answer index: 'A' or 'B'.

Sentence: Milo knows that a frozen lake is smoother than a grass field. This means that when he slides his paper plane across one of the two surfaces it will experience less friction. Question: Which surface is that? (A) frozen lake (B) grass field
Output:
A