You are given a science question (easy-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]: A student walking quickly while carrying an orange on his lunch tray stops suddenly. The orange will most likely roll off the tray due to  
 (A) inertia of the orange. (B) centripetal force of the orange. (C) the friction acting on the orange. (D) the balanced forces acting on the orange.
[EX A]: A

[EX Q]: What property is the same for each atom of an element?  
 (A) energy (B) mass number (C) atomic number (D) number of neutrons
[EX A]: C

[EX Q]: Actin filaments are part of the contractile machinery in smooth muscle cells of eukaryotic organisms. Which organelle is responsible for contractile movement in these cells?  
 (A) nucleus (B) cytoskeleton (C) endoplasmic reticulum (D) plasma membrane
[EX A]:
B