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.

[Q]: 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
[A]: A


[Q]: Which of the following best describes a role of mushrooms in ecosystems?  
 (A) capturing energy from sunlight (B) consuming living plant material (C) taking energy from animal hosts (D) breaking down dead plant material
[A]: D


[Q]: Which part of Earth's structure is composed of a solid mixture of nickel and iron?  
 (A) the inner core (B) the outer core (C) the lithosphere (D) the asthenosphere
[A]:
A