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]: A population of plants growing on an island consisted of two varieties, one with thorns and the other without. Over a period of many years, the variety with thorns gradually disappeared. Which process most likely brought about this change in the plant population?  
 (A) gene flow (B) genetic drift (C) natural selection (D) random mutation
[A]: C


[Q]: Which is the best evidence for the theory of continental drift?  
 (A) the appearance of volcanoes at the boundaries where plates collide (B) earthquakes at boundaries where one plate slides past another (C) cases where a species exists in only one isolated place (D) fossils of the same species found on widely separated continents
[A]: D


[Q]: A student drops a ball. Which force causes the ball to fall to the ground?  
 (A) electricity (B) friction (C) gravity (D) magnetism
[A]:
C