You are given a science question (hard-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:
Janette conducts an investigation to see which foods make her feel more fatigued. She eats one of four different foods each day at the same time for four days and then records how she feels. She asks her friend Carmen to do the same investigation to see if she gets similar results. Which would make the investigation most difficult to replicate?
(A) measuring the amount of fatigue (B) making sure the same foods are eaten (C) recording observations in the same chart (D) making sure the foods are at the same temperature

Ex Output:
A

Ex Input:
If a child scrapes his foot on a piece of rusty metal, it is important to get medical treatment because the
(A) metal is corrosive to the skin. (B) foot carries large amounts of bacteria. (C) foot is the most sensitive part of the body. (D) metal may be contaminated and cause infection.

Ex Output:
D

Ex Input:
From year to year, farmers rotate different crops in the fields to improve soil nutrients. Why is crop rotation also an effective pest management method?
(A) It allows chemicals to kill more pests. (B) It creates crops that are pest-resistant. (C) It interrupts the life cycles of pests. (D) It allows pests to overpopulate.

Ex Output:
C