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.

Input: Consider Input: Which object is best used to demonstrate the bending of light as it passes through a substance?  
 (A) convex lens (B) flat mirror (C) opaque rod (D) concave mirror

Output: A


Input: Consider Input: After a star runs out of most of its hydrogen fuel, it becomes hotter and more luminous. What stage does this represent in the life cycle of a star?  
 (A) quasar (B) protostar (C) red giant (D) white dwarf

Output: C


Input: Consider Input: The water contained in a geyser system gains energy from the underground material surrounding it. The water molecules gain kinetic energy and this results in an increase in the pressure of the water. Eventually the geyser erupts and expels water into the air above ground. Which of the following types of energy is the source for the initial energy gain of the water?  
 (A) electrical (B) magnetic (C) mechanical (D) thermal


Output: D