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.
--------
Question: What property is the same for each atom of an element?
(A) energy (B) mass number (C) atomic number (D) number of neutrons

Answer: C

Question: Seismic waves occur as a result of an earthquake. Which statement describes a wave property that makes it possible for scientists to locate the source of an earthquake?
(A) The wavelength of a wave is measured from crest to crest. (B) Waves travel uniformly outward from the wave source. (C) The frequency of waves varies in different mediums. (D) Waves move at the same speed in different materials.

Answer: B

Question: Based on the evidence available at the time, early models of the solar system stated that all objects in space orbited Earth. In the 16th century, an astronomer reevaluated the evidence and proposed a model of the solar system that is still in use. What part of this model corrected the mistake in previous solar system models?
(A) The Sun is at the center of this model. (B) Earth is the largest object in this model. (C) This model contains more than one star. (D) This model shows that Earth is stationary.

Answer:
A