TASK DEFINITION: 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.
PROBLEM: The engineering team that is designing a scientific research station on the Arctic permafrost has to provide the station with energy for cooking, heating, and lighting. Considering the fragile environment and other conditions there, the best choice is probably to  
 (A) build a wind turbine. (B) have fuel trucked in. (C) have a pipeline built. (D) build a solar collector.

SOLUTION: A

PROBLEM: What gas in the air do we need to breathe in order to live?  
 (A) nitrogen (B) oxygen (C) carbon dioxide (D) hydrogen (E) water vapor

SOLUTION: B

PROBLEM: Which human body system forms a barrier between internal body structures and the external environment?  
 (A) nervous (B) digestive (C) circulatory (D) integumentary

SOLUTION:
D