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.

[EX 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
[EX A]: D

[EX Q]: Which form of energy are x rays and ultraviolet light?  
 (A) nuclear (B) heat (C) electromagnetic (D) chemical
[EX A]: C

[EX Q]: Scientists use the term "light year" to describe  
 (A) how fast light travels in space. (B) the distance light travels in one year. (C) how large the diameters of different stars are. (D) the time it takes the Sun to move through the galaxy.
[EX A]:
B