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.

Which organ is made mostly of muscle?  
 (A) heart (B) lung (C) ear (D) brain
A

A student measured liquid with a graduated cylinder. Which of the following units could be used to record the volume of the liquid?  
 (A) pounds (B) meters (C) grams (D) milliliters
D

The items listed below were found in a science classroom. * a heart made of plastic with many of its parts labeled * clay formed to look like Earth and other planets * a giant plastic plant cell with removable cell parts These items are all examples of  
 (A) models (B) experiments (C) variables (D) controls

A