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: Evidence of organisms that lived on Earth a long time ago would most likely be found in  
 (A) crystals. (B) lava. (C) sedimentary rock. (D) metamorphic rock.

Answer: C


Question: When iron combines with oxygen in a moist environment, rust forms because of a  
 (A) chemical reaction. (B) physical reaction. (C) change in density. (D) change in temperature.

Answer: A


Question: Male barn swallow birds with symmetrically-shaped wings find mates more quickly than males with asymmetrical wing shapes. Which statement best explains the significance of symmetry in the barn swallow population?  
 (A) Symmetrical wings are attractive to females. (B) Symmetrical wings indicate genetic mutations. (C) Symmetrical wings indicate that males are good predators. (D) Symmetrical wings are signs that a bird is very aggressive.

Answer:
A