Q: 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.
Certain flowers will open for twelve hours and then close. Which stimulus do the flowers respond to when they open and then when they close for that time period?
(A) light levels (B) moon phases (C) seasonal temperatures (D) carbon dioxide levels
A:
A