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]: A student plans to grow algal colonies in solutions with different concentrations of liquid fertilizer. Which is a clear and testable hypothesis to guide this investigation?  
 (A) Algae like fertilizer. (B) Fertilizer is good for algae. (C) Fertilizer improves the genetic traits of algae. (D) Algal growth rate increases with fertilizer concentration.
[EX A]: D

[EX Q]: A teacher breaks a bar of pure copper into two different sized pieces. Which is the most likely difference between the two pieces?  
 (A) mass (B) texture (C) boiling point (D) melting point
[EX A]: A

[EX Q]: What is the main function of scales on a fish?  
 (A) to protect the fish (B) to attract predators (C) to help the fish find food (D) to help the fish breathe
[EX A]:
A