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.

Q: The force of an object, with a certain mass accelerating at a certain rate, can be determined by using the equation below. force = mass x acceleration Which object would have the greatest force?  
 (A) a 5-kg object accelerating at 10 m/s^2 (B) a 5-kg object accelerating at 20 m/s^2 (C) a 20-kg object accelerating at 4 m/s^2 (D) a 20-kg object accelerating at 3 m/s^2

A: B
****
Q: 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

A: C
****
Q: Human actions affect the environment. Which human action affects the smallest area of the environment?  
 (A) burning a forest (B) burning fossil fuels (C) digging a new landfill (D) spraying crops with chemicals

A:
C
****