TASK DEFINITION: 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.
PROBLEM: Which characteristic best identifies a pure substance?
(A) shape (B) texture (C) melting point (D) state of matter

SOLUTION: C

PROBLEM: Which difference between water and ice results in ice floating on cold water?
(A) heat (B) shape (C) density (D) volume

SOLUTION: C

PROBLEM: Human actions can change the rate at which soil erodes. Which of the following would most likely slow the rate of soil erosion?
(A) applying nitrogen-rich fertilizers (B) keeping grasses trimmed short (C) building houses on stilts (D) planting trees along cliffs

SOLUTION:
D