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]: Why would animals most likely have to leave an area during a drought?  
 (A) to find mates (B) to find shelter (C) to escape predators (D) to find water and food
[EX A]: D

[EX Q]: In any ecosystem, organisms interact with biotic and abiotic parts of the environment. As a result of all of the interactions, the matter within the system is  
 (A) produced when plants grow. (B) recycled when organisms die. (C) lost when animals and plants die. (D) formed when new animals are born.
[EX A]:
B