B, when humans exhale we put out carbon dioxide.
Answer:
It is better to compare the average height gain of control and experimental groups of plants to eliminate all other variables.
Explanation:
If you evaluate individual plants, the data may vary. The experimental group is the one where an experimental procedure is performed while the control group does not receive any treatment.
This is because these species would not have been studied much or documented in the past because of their inaccessibility. Many species may be unknown to science, but that does not mean they are unknown to humans. Traditional knowledge within rural areas may have knowledge of these species, but the remoteness of these areas means that universities and research centres may not have sent scientists into these areas.
Small rocky bodies that revolve around the sun are asteroid's