What are the main characteristics of cnidarians?

I- They include corals, anemones, hydras, and jellyfish.
II- They are all marine animals, except for the hydra, which is freshwater.
III- They have cnidocytes, which are urticating cells located on the surface of their body and which serve to inject venom into their prey.
IV- They have radial symmetry and their cells are organized into poorly developed tissues.
V- Most have a hydrostatic skeleton, that is, they maintain their shape by the accumulation of water inside.
a) I, II, and IV are correct.
b) II, III, and V are correct.
c) I, III, and V are correct.
d) I, II, III, IV, and V are correct.