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.

Let me give you an example: Sentence: Jacob and Benny are squatting at the gym. Jacob has thin frail legs and Benny has big strong legs. Question: Who squats less weight? (A) Jacob (B) Benny
The answer to this example can be: Jacob
Here is why: Typically, people with thin frail legs squat less weight than people with big strong legs, so the answer is Jacob.

OK. solve this:
Sentence: A valley is significantly rougher than a mountainside. Question: This means that lava rolling down which surface will reach a greater top speed? (A) mountainside (B) valley
Answer:
valley