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 force produces energy as heat?  
 (A) pull (B) gravity (C) friction (D) magnetic
C

Campers shouted toward a canyon wall. What characteristic of sound best explains why the campers heard an echo?  
 (A) Sound waves traveled slowly down the canyon. (B) Sound waves were absorbed by the canyon wall. (C) Sound waves reflected off the canyon wall. (D) Sound waves were refracted around the canyon.
C

Some meteorologists use visual aids such as diagrams, maps, and charts when they present the weather to television viewers. How do different types of visual aids help the viewers understand complex weather phenomena?  
 (A) by combining knowledge from past reports with new information (B) by providing information collected by other meteorologists (C) by checking the accuracy of each part of the weather report (D) by showing many components that impact the weather

D