Phytoplanktonic Organisms?

Question

Which of the following statements concerning living phytoplanktonic organisms are true?
1. They are important members of communities surrounding deep-sea hydrothermal vents.
2. They are important primary producers in most aquatic food webs.
3. They are important in maintaining oxygen in Earth's seas and atmosphere.
4. They are most often found growing in the sediments of seas and oceans.
5. They can be so concentrated that they affect the color of seawater.

A. 2, 3, and 5
B. 1 and 4
C. 2, 3, and 4
D. 1, 2, and 4
E. 3, 4, and 5


I know choice 5 is true so now I'm stuck between A and E. Please help.

Answer 1

The answer is A. Phytoplanktons are primer producers that live at the surface of the ocean, because they need sunlight for photosynthesis.

Answer 2

Blue whales are carnivores. They eat massive amounts of krill but also eat the small fish, crustaceans, and squid caught up with the krill.