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.

Q: Two pieces of the same metal are placed on a table. The pieces of metal have the same density, mass, and texture. Which characteristic must be the ONLY difference between the two samples?  
 (A) They have different dimensions. (B) They have different boiling points. (C) They are made up of a different type of matter. (D) They contain a different amount of matter per unit volume.

A: A
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Q: Rhinoceroses and horses are related. They have very similar digestive systems and an odd number of toes on their feet. Horses have one toe, and rhinoceroses have three. These facts best support which claim?  
 (A) Horses and rhinoceroses share a common ancestor. (B) Horses and rhinoceroses are genetically identical. (C) Horses are the ancestors of modern rhinoceroses. (D) Horses have descended from modern rhinoceroses.

A: A
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Q: Which of these is a physical change that takes place in a garden?  
 (A) Insects eat the leaves of a plant for food. (B) Flowers grow after a summer rain shower. (C) Earthworms loosen soil as they travel through it. (D) Leaves convert sunlight to sugar by photosynthesis.

A:
C
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