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.

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

Which of the following statements best explains how the decomposition of plant and animal matter helps to form rich soils?
(A) Decomposition adds silt to soil. (B) Decomposition adds water to soil. (C) Decomposition adds oxygen to soil. (D) Decomposition adds nutrients to soil.
D

Marta and Roger are comparing how long it takes two different types of seeds to sprout. They plant both types of seeds in similar pots, place them in a sunny window, and water them daily. If they want to conduct their investigation correctly, which information is most important to record?
(A) the depth of the soil (B) the temperature of the water (C) the number of days until the seeds sprout (D) the size of pot used for growing the seeds
C