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: Sir Isaac Newton stated that every object in the universe attracts matter. The attraction depends on the mass of an object and the distance between the objects. What type of force did Newton describe?  
 (A) centripetal force (B) generalized force (C) centrifugal force (D) gravitational force

A: D
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Q: Some plant species are more tolerant of acidic soil than others. The tolerant species are favored in areas affected by which consequence of human activity?  
 (A) mixing of pollutants with rain (B) erosion of topsoil by clearcutting (C) runoff of fertilizer used in farming (D) thinning of the atmospheric ozone layer

A: A
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Q: The finest-grained soils are richest in  
 (A) sand. (B) humus. (C) clay. (D) iron.

A:
C
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