Answer: The correct answer is-
C) insects and zooplankton.
Primary consumer are those organisms that consume producers ( autotrophs such as phytoplanktons and photosynthetic bacteria) that is they occupy the second trophic level ( the first being occupied by autotrophs) in a food chain within an ecosystem.
In an aquatic food chain, insects and zooplankton consume phytoplanktons ( autotrophs) and are considered as primary consumer.
Thus, option C) is the right answer.