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]: Which statement best describes how birth and death rates compare in a population at carrying capacity?
(A) The birth rate is greater than the death rate. (B) The birth rate is less than the death rate. (C) The birth rate is equal to the death rate. (D) The birth rate and the death rate are zero.
[EX A]: C

[EX Q]: To study the effect of heat on plant growth, Andy divided ten identical seedlings into groups. She placed one group on a windowsill in the sun and the other group in a dark closet on the cool (north) side of the house. Think about the characteristics of a properly designed scientific experiment. What is wrong with the above experiment?
(A) The temperature difference between the two groups was not great enough. (B) The amount of light was different for the two groups. (C) One group of seedlings got less water than the other. (D) Nothing is wrong with the experiment.
[EX A]: B

[EX Q]: Some types of bacteria can only live where oxygen is not present. These bacteria were well adapted to life on Earth over 2 billion years ago. Which of the following changes caused many of these bacteria to become extinct?
(A) the slow movement of tectonic plates (B) the varying temperatures of each season (C) an increase in volcanic activity under the oceans (D) an increase in the number of photosynthetic organisms
[EX A]:
D