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.

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

Which of the following compounds is most likely to be part of living organisms?  
 (A) C?H??O? (B) BF? (C) MoCl? (D) CsI
A

Which of the following describes condensation?  
 (A) a liquid changing to a solid (B) a solid changing to a liquid (C) a solid changing to a gas (D) a gas changing to a liquid

D