I think answer is B. Sorry if it is wrong.
all of them because they have to work together in order to do its job
Answer:
Ideally, the experimental and control groups are identical. As much as possible, the two groups should overlap in every characteristic.
Explanation:
At the beginning of your study, you need your two groups to be as statistically similar as is humanly possible. That way, when you control for other variables, you can reasonably attribute any statistically significant differences at the end of the study to your intervention.
Explanation:
Variations in the sun's energy reaching Earth
Changes in the reflectivity of Earth’s atmosphere and surface
Changes in the greenhouse effect, which affects the amount of heat retained by Earth’s atmosphere
