You are presented with the quiz "what do fish feed on?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "phytoplankton are bacteria and algae that use sunlight to make food" and "since fish feed on phytoplankton, they are drawn to phytoplankton-rich waters". So, what's the best answer to the question?

Select from the following. 1. rocks. 2. embryos. 3. pizza. 4. algae. 5. energy. 6. insects. 7. gills. 8. food.
Answer:
4.