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.
--------
Question: How are green plants an important part of the carbon dioxide-oxygen cycle?
(A) They add oxygen to the soil. (B) They release oxygen into the air. (C) They fix carbon dioxide in the soil. (D) They store carbon dioxide in roots.

Answer: B

Question: Which of the following is a step in the life cycle of an apple tree?
(A) Eggs grow from seedlings. (B) Fruit forms flowers. (C) Seedlings grow from leaves. (D) Fertilized flowers form fruit.

Answer: D

Question: A scientist claims that he made a discovery in the lab. What does the scientist need to have in order to prove that the discovery is valid?
(A) diagrams showing the steps used in the discovery (B) accurate records that show that the data are consistent (C) documents showing that the scientist is well known (D) proof that the equipment used in the discovery is of high quality

Answer:
B