Concept:Floating microscopic organisms are categorised by their mode of nutrition.
Those that feed on other organisms are heterotrophs.
Explanation:Phytoplankton are microscopic and float, but they are autotrophs because they produce their own food through photosynthesis.
Zooplankton are microscopic, floating organisms that consume other organisms, making them heterotrophs.
Hence, floating microscopic heterotrophs are grouped as zooplankton.
Microbes is a broader term that includes both autotrophs and heterotrophs.
Nekton are actively swimming aquatic organisms, not microscopic floaters.
Answer:B. zooplankton