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.

Q: Which of the following units best represents the density of an object?
(A) kg (B) hr (C) m/s^2 (D) g/cm^3

A: D
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Q: Which set contains kingdoms that contain only heterotrophs?
(A) Protists, Fungi (B) Bacteria, Animals (C) Plants, Fungi (D) Animals, Fungi

A: D
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Q: Which planet is fourth from the Sun in our solar system?
(A) Mars (B) Earth (C) Venus (D) Jupiter

A:
A
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