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]: Which of these is a property of water that allows it to transport materials through the Earth system?  
 (A) It expands as it solidifies. (B) It is transparent. (C) It dissolves many substances. (D) It is a compound.
[EX A]: C

[EX Q]: Which body system's primary function is the continuation of the species?  
 (A) digestive (B) nervous (C) excretory (D) reproductive
[EX A]: D

[EX Q]: Where is the smallest negatively-charged particle found in an atom?  
 (A) nucleus (B) orbits in the nucleus (C) orbits around the nucleus (D) between the proton and neutron
[EX A]:
C