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.

[EX Q]: What happens when water flows over a rock for a long period of time?  
 (A) erosion (B) flooding (C) breakage (D) evaporation
[EX A]: A

[EX Q]: Which illustrates the correct order of relationships in organisms?  
 (A) tissue -> organ system -> organ -> cell (B) organ -> cell -> organ system -> tissue (C) cell -> tissue -> organ -> organ system (D) organ system -> organ -> cell -> tissue
[EX A]: C

[EX Q]: What is the smallest particle of the element gold (Au) that can still be classified as gold?  
 (A) atom (B) molecule (C) neutron (D) proton
[EX A]:
A