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: Florida has a large supply of phosphate that ancient seas deposited millions of years ago. The phosphate contains the remains of animals that were deposited in layers on the sea floor. Which type of rock did the phosphate become?  
 (A) intrusive igneous (B) extrusive igneous (C) clastic sedimentary (D) organic sedimentary

A: D
****
Q: Which most likely contributed to the extinction of many species and endangered the survival of others?  
 (A) pollution (B) habitat destruction (C) an asteroid hitting Earth (D) tectonic plate movement

A:
B
****