TASK DEFINITION: You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.
PROBLEM: Several species of fish live in a classroom aquarium. Students notice that the gills of one type of fish move faster than the gills of the other fish. Which of these statements is the best hypothesis on this observation?  
 (A) Fish have a two-chambered heart. (B) Some fish are much larger than others. (C) Fish need different amounts of oxygen. (D) There are six types of fish in the aquarium.

SOLUTION: C

PROBLEM: Which characteristic property indicates that igneous rock cools slowly?  
 (A) mineral composition (B) hardness (C) density (D) crystal size

SOLUTION: D

PROBLEM: Which material should be used on a bicycle ramp to increase friction?  
 (A) shiny metal (B) rough paper (C) smooth wood (D) wet plastic

SOLUTION:
B