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]: The basic life functions of an organism are carried on by  
 (A) cells (B) nutrients (C) atoms (D) hormones
[A]: A


[Q]: The body is made up of many systems that interact with one another. For example, the skeletal system and the muscular system work together to help the body move. Which system works with the respiratory system to distribute oxygen to the body?  
 (A) muscular system (B) digestive system (C) lymphatic system (D) circulatory system
[A]: D


[Q]: During a biochemical reaction, pyruvate (C3H4O3) is converted into carbon dioxide (CO2) and water (H2O). In what cellular organelle does this biochemical reaction occur?  
 (A) nucleus (B) cytoplasm (C) mitochondria (D) endoplasmic reticulum
[A]:
C