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.

[Q]: Which part of an atom is involved in chemical reactions?  
 (A) nucleus and its particles (B) negatively-charged particles (C) neutrally-charged particles (D) positively-charged particles
[A]: B


[Q]: Which unit is used to indicate the amount of energy in food?  
 (A) ounce (B) degree (C) calorie (D) gram
[A]: C


[Q]: After a volcanic eruption, it takes a long time for large ecosystems to fully recover. Which statement best explains why the development takes so long?  
 (A) Space is limited for growth. (B) The quality of light is low. (C) Soil must be created. (D) Minerals are destroyed.
[A]:
C