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.

[Q]: An athlete can run 9 kilometers in 1 hour. If the athlete runs at that same average speed for 30 minutes, how far will the athlete travel?      
 (A) 18 kilometers (B) 9 kilometers (C) 4.5 kilometers (D) 3.3 kilometers
[A]: C


[Q]: The skin is the largest organ in the human body. Why is skin considered to be an organ?  
 (A) It is made of cells. (B) It acts as a barrier. (C) It is made of tissues. (D) It is part of an organism.
[A]: C


[Q]: Which of these will result in the least gravitational attraction?  
 (A) two 2g objects 2 meters apart (B) two 2g objects 4 meters apart (C) two 1g objects 6 meters apart (D) two 1g objects 8 meters apart
[A]:
D