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 Input:
A drug company developed a pill to reduce cases of stomach virus. To test the medication, half of the participants got the pill with the new medicine and half got a sugar pill. Which term best identifies the participants who got a sugar pill?  
 (A) control (B) experimental (C) dependent variable (D) independent variable

Ex Output:
A


Ex Input:
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.

Ex Output:
C


Ex Input:
Human Immunodeficiency Virus (HIV) infects the cells that coordinate the human immune response. When these cells are killed or compromised, the body cannot effectively protect itself from infection. Which cells does HIV infect?  
 (A) natural killer T cells (B) regulatory T cells (C) cytotoxic T cells (D) helper T cells

Ex Output:

D