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 Q]: 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 A]: D

[EX Q]: A research study concluded that people who work longer hours increase their chances of having higher blood pressure. This conclusion was developed from a study of 200 men of different ages. How is this investigation biased?
(A) The sample size was too large. (B) Scientists did not run the study. (C) Women were excluded from the study. (D) No medication was given to the men.
[EX A]: C

[EX Q]: The classification of some organisms has changed. Which new process is used to reclassify organisms?
(A) Organisms are now given Latin-based scientific names. (B) Structures are now examined at the molecular level. (C) Organisms are now divided into three kingdoms. (D) Structures are now used to classify organisms.
[EX A]:
B