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.
One example is below.
Q: Which part of a bicycle BEST moves in a circle? 
 (A) Seat (B) Frame (C) Foot pedal (D) Kickstand
A: C
Rationale: Seat, frame and Kickstand are static parts of the bicycle, even when bicycle moves. Foot pedal moves in a circle as bicycle moves.
Q: Rocks can be classified many different ways, including as igneous, metamorphic, and sedimentary. This classification is based on the  
 (A) origin of the rocks. (B) use of the rocks. (C) size of the rocks. (D) hardness of the rocks.
A:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
A