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]: 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.
[EX A]: C

[EX Q]: A student poured water into a plastic tray. The student then put the tray into the freezer. What property of the water changed as the water froze?  
 (A) The water became a gas. (B) The mass of water increased. (C) The water took a definite shape. (D) The flavor of the water changed.
[EX A]: C

[EX Q]: Some non-native plants can adapt to their environments more quickly than some native plants or crops can. Which adaptation would most likely decrease a plant's ability to survive?  
 (A) having a large number of seeds (B) having a resistance to herbicides (C) having roots that develop rapidly (D) having leaves that form at a slow rate
[EX A]:
D