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: Which is an example of a chemical reaction?
(A) Vinegar added to baking soda forms a gas. (B) Water evaporates into air. (C) Sugar dissolves in water. (D) Corn kernels are crushed to form flour.

SOLUTION: A

PROBLEM: Proxima Centauri is the closest star to the Sun. Which units do astronomers most often use for the distance between Earth and Proxima Centauri?
(A) miles (B) meters (C) light years (D) astronomical units

SOLUTION: C

PROBLEM: The speed and general direction of motion of a galaxy relative to the Earth can be determined by
(A) measuring its red shift. (B) the gravity it exerts. (C) contrasting it against nearby stars. (D) observing its motion across the sky.

SOLUTION:
A