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: What best explains why some cooking pans have rubber handles?  
 (A) The rubber in the handles is easy to hold. (B) The rubber in the handles is a good insulator. (C) The rubber in the handles keeps the food in the pan hot. (D) The rubber in the handles keeps the metal in the pan cool.
Example Output: B

Example Input: Electric circuits provide energy for lightbulbs. Which of these prevents the flow of electrons?  
 (A) a circuit that is closed (B) a series circuit (C) a circuit that is open (D) a parallel circuit
Example Output: C

Example Input: When a chicken egg was placed in a beaker of vinegar, bubbles formed on the eggshell. After twenty-four hours, the eggshell is no longer present. Which statement is an observation?  
 (A) Gravity made the egg sink to the bottom of the beaker. (B) The vinegar caused the eggshell to dissolve. (C) The egg was denser than the vinegar. (D) Bubbles appeared on the eggshell.
Example Output:
D