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: Of these research projects, which is the best choice for a student who is interested in environmental issues to study?  
 (A) making cars run on less fuel (B) finding more sites for copper mines (C) making ocean liners bigger and faster (D) replacing human workers with robots

SOLUTION: A

PROBLEM: If an atom has two protons and three electrons, then the atom is  
 (A) positively charged. (B) negatively charged. (C) radioactive. (D) neutral.

SOLUTION: B

PROBLEM: The suspension system of a truck includes the  
 (A) engine and carburetor. (B) wheels and axles. (C) brakes and muffler. (D) steering wheel and speedometer.

SOLUTION:
B