You are given a sentence and a question. You're expected to write the correct answer based on the sentence.
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Question: Sentence: A valley is significantly rougher than a mountainside. Question: This means that lava rolling down which surface will reach a greater top speed?

Answer: valley

Question: Sentence: John throws a rubber ball and a glass ball against a brick wall. Question: Which ball is least likely to break?

Answer: Rubber ball

Question: Sentence: Jimbo knows that the surface of his coffee table isn't as rough as the surface of his floor. Question: When he slides his doily across both surfaces, which will force the doily to travel at a lower rate of speed?

Answer:
floor