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.

Use the information below to answer the question. Many people are concerned that the reduction in the number of acres of forested area on Earth will lead to a large reduction in the amount of oxygen in Earth's atmosphere. If this happens, an organism's ability to breathe would be affected. The effect would be similar to moving the organism from
(A) sea level to a mountaintop. (B) sea level to a valley below sea level. (C) a mountaintop to sea level. (D) a beach at sea level to a valley at sea level.
A