Final answer:
Multilevel selection/cooperation occurs in bacteria, plants, and humans, promoting energy and matter efficiency. Bacteroides in the human gut and nitrogen fixing bacteria in the soil are examples of cooperation in bacteria and plants.
Step-by-step explanation:
The concept of multilevel selection or cooperation has been documented in a wide variety of organisms including bacteria, plants, and humans. This kind of cooperative interaction promotes efficiency in the use of energy and matter within organisms. Examples of this include bacteria in the human gut working symbiotically with a host (Bacteroides are prevalent in the human gut), plants benefiting from nitrogen fixing bacteria in the soil, and humans working in groups, which has been essential for survival and social development. The correct answer to the question "Multilevel selection/cooperation has been documented in ________." is D) All of the above.