TASK DEFINITION: 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.
PROBLEM: 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

SOLUTION: C

PROBLEM: Which term best describes the nature of all light waves?  
 (A) longitudinal (B) transverse (C) compressional (D) magnetic

SOLUTION: B

PROBLEM: Where in the periodic table would shiny, malleable materials used in making jewelry be found?  
 (A) group 1 (1A) (B) group 4 (4A) (C) group 11 (1B) (D) group 17 (7A)

SOLUTION:
C