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.

Example Input: Which example best illustrates an action-at-a-distance force?  
 (A) lifting a box (B) an apple falling (C) pulling a nail out of wood (D) a car moving along a flat surface
Example Output: B

Example Input: In pea plants, the allele for smooth peas is dominant (S). If a heterozygous smooth pea plant (Ss) is crossed with a homozygous smooth pea plant (SS), which are the possible genotypes the offspring could have?  
 (A) only SS (B) only Ss (C) Ss or SS (D) ss or SS
Example Output: C

Example Input: Hydrogen has an atomic mass of 1, and oxygen has an atomic mass of 16. When a water molecule forms, two hydrogen atoms combine with one oxygen atom. What is the mass of a water molecule?  
 (A) 14 (B) 16 (C) 17 (D) 18
Example Output:
D