TASK DEFINITION: You are given a science question (hard-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.
PROBLEM: A car tire runs over a can and crushes it completely. Which statement is true for the atoms of the structure of the can?  
 (A) The atoms are broken. (B) The atoms are flattened. (C) The atoms remain the same. (D) The atoms are changed into different atoms.

SOLUTION: C

PROBLEM: One type of cold remedy is an effervescent tablet that breaks down in water. When the tablet is placed in water, it forms gas bubbles. In this example, the formation of a gas  
 (A) is a physical property. (B) occurs when adding water to acid. (C) is a sign of a chemical change. (D) occurs when the water boils.

SOLUTION: C

PROBLEM: In a healthy forest, dead trees and limbs fall to the ground and decompose. Which of these statements best describes why decomposition is important to a forest ecosystem?  
 (A) Nutrients are released when wood is broken down. (B) Worms produce oxygen used by other organisms. (C) Dead trees provide nest sites for many different species of birds. (D) Water is stored in dead trees and limbs.

SOLUTION:
A