For the last question it's either C or D.
Atria is a large part of the heart so too big for cells; arteries & veins lead away or to the heart.
Capillaries are the smallest vascular structures that allow materials to be exchanged easily between cells.
Answer:
A Starfish is Triploblastic meaning they consist of three germ layers. Hydra are diploblastic meaning they consist of only 2 germ layers.
The Nucleus is separated from the cell’s cytoplasm by a
membrane. The nucleus contains hereditary materials made of plenty proteins and
DNA. The nucleus directs all cell activities. Nucleus is commonly found in
Eukaryotic cells. The genetic materials found in the Nucleus is organized as
DNA molecules, together with a wide array of proteins, which causes to form
chromosomes.