You are given a science question (hard-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 Input:
Of these research projects, which is the best choice for a student who is interested in environmental issues to study?  
 (A) making cars run on less fuel (B) finding more sites for copper mines (C) making ocean liners bigger and faster (D) replacing human workers with robots

Ex Output:
A


Ex Input:
Carolina wrens and painted buntings are two bird species that live in overlapping territories. They have different requirements for food and nesting. Which term best describes the relationship between the two species?  
 (A) parasitism (B) symbiosis (C) coexistence (D) mutualism

Ex Output:
C


Ex Input:
Mosquito fish found on the islands of the Bahamas live in various isolated freshwater ponds that were once a single body of water. When several male and female mosquito fish are taken from two isolated ponds and placed into a single pond, the breeding preference of each mosquito fish is for fish from its own original pond. Which of these most likely resulted in this breeding preference?  
 (A) Availability of food influenced the breeding preferences of the fish. (B) Competition for a suitable mate influenced the breeding preferences. (C) Predators in the pond influenced the breeding preferences of the fish. (D) Speciation due to reproductive isolation influenced the breeding preferences.

Ex Output:

D