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 is a main feature of plains?  
 (A) a flat, level surface (B) a high, steep peak (C) a low, shallow basin (D) a gentle, gradual slope
[EX A]: A

[EX Q]: What procedure should be performed after any handling of a plant sample in a lab?  
 (A) applying disinfectant to the counters (B) throwing away plant material in the trash (C) washing hands with an antibacterial soap (D) placing hands under an ultraviolet light
[EX A]: C

[EX Q]: A student picked up a small rock using a magnet. The rock probably contained  
 (A) quartz. (B) diamond. (C) aluminum. (D) iron.
[EX A]:
D