Aerial metagenomics' best refers towhich one of the following situations?

1. A

   Collecting DNA samples from air in a habitat at one go

   Collecting DNA from air in a habitat in one go. That is aerial metagenomics.

2. B

   Understanding the genetic makeup of avian species of a habitat

   Genetic makeup of birds. Ornithology, not this term.

3. C

   Using air-borne devices to collect blood samples from moving animals

   Airborne blood sampling. Not the method.

4. D

   Sending drones to inaccessible areas to collect plant and animal samples from land surfaces and water bodies

   Drones collecting bulk samples. Field logistics, not metagenomics of air.

Summary. Official key is (a). Aerial metagenomics samples environmental DNA/RNA from air — a snapshot of the organisms shedding genetic material in that habitat. It is not a bird genome project, dart-sampling, or drone fieldwork as such.