Answer:
The answer is choice A. producer.
Step-by-step explanation:
Phytoplankton are single-celled photosynthetic organisms often found in the ocean. They live in a special section of the sea called the photic zone of the ocean, in which photosynthesis is possible. They are organisms that give energy to others and are placed at the bottom of the food chain/food web, thus making them producers.
Fun Fact: Phytoplankton are classified/labeled as primary producers, which means they stand as the basis or basic foundation of the food chain/food web. They are crucial to the survival of their ecosystem. Without them, the environment cannot survive and thrive. (This also means much of the marine ecosystems we know today wouldn't be nearly as luscious and promising as they are without the primary producer phytoplankton.)
In case you want more proof: