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: When a hammer strikes a nail, the nail  
 (A) exerts balanced forces that helps it from moving. (B) exerts a force equal to the weight of the hammer. (C) exerts an unbalanced force that changes its velocity. (D) exerts an equal and opposite force back on the hammer.

A: D
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Q: Human DNA includes a class of genes called "tumor suppressors." What do these genes do in bone cells?   
 (A) They restrict cell cycle progression in bone cells. (B) They promote the rapid development of bone cells. (C) They limit the number of bones in the human body. (D) They enable phosphorus and calcium to enter bone cells.

A: A
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Q: Two species of garter snake in the genus Thamnophis originated from a single ancestor. These two species live in the same geographic area, however, one lives in arid land and the other lives in water.Which of the following best identifies the cause of speciation between these two garter snakes?  
 (A) mechanical isolation (B) behavioral isolation (C) habitat isolation (D) allopatric isolation

A:
C
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