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]: Organisms contribute to the water cycle mainly through the process of  
 (A) irrigation. (B) evaporation. (C) precipitation. (D) transpiration.
[EX A]: D

[EX Q]: Which best describes a scientific theory?  
 (A) It is still being tested. (B) It is true, once written. (C) It is different for each continent. (D) It is determined in a court of law.
[EX A]: A

[EX Q]: Which of the following happens only during the adult stage of the life cycle of a frog?  
 (A) A frog lays eggs. (B) A frog swims in water. (C) A frog begins to lose its tail. (D) A frog begins to develop lungs.
[EX A]:
A