The Following Questions Refer to the Paragraph Below

The following questions refer to the paragraph below.
An elementary school science teacher decided to liven up the classroom with a salt-water aquarium. Knowing that salt-water aquaria can be quite a hassle, the teacher proceeded stepwise. First, the teacher conditioned the water. Next, the teacher decided to stock the tank with various marine invertebrates, including a polychaete, a siliceous sponge, several bivalves, a shrimp, several sea anemones of different types, a colonial hydra, a few coral species, an ectoproct, a sea star, and several gastropod varieties. Lastly, some vertebrates-a parrotfish and a clownfish-were added. She arranged for daily feedings of copepods and feeder fish.
-The bivalves started to die one by one; only the undamaged shells remained. To keep the remaining bilvalves alive, the teacher would have had to remove the

A) sea anemones.
B) sea star.
C) gastropods.
D) ectoprocts.
E) parrotfish.