TASK DEFINITION: You are given a science question (easy-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: The shape of a riverbed changes over time as a result of which gradual process?  
 (A) erosion (B) dissolving (C) plate shifting (D) compaction

SOLUTION: A

PROBLEM: Which would be a safe practice to exercise during laboratory investigations?  
 (A) using open flames to heat all materials (B) keeping your cell phone on the laboratory countertop (C) knowing where your instructor/laboratory leader is at all times (D) removing your safety glasses when moving from station to station

SOLUTION: C

PROBLEM: What is at the center of our solar system?  
 (A) a medium planet with an atmosphere. (B) a star composed of carbon and nitrogen. (C) a black hole that was once a star. (D) a star composed of hydrogen and helium.

SOLUTION:
D