The poisonous fluid present in the nematocyst of $Hydra$ is

Hydra will regenerate from a fragment,if it contains:

Which of the following is a characteristic feature of the phylum $Coelenterata$ (Cnidaria)?

What is the function of nematocysts in the phylum $Cnidaria$?

How many ova are formed in the ovary of Hydra?

Which of the following cells are present only in the epidermis of Hydra?
$(A)$ Interstitial cells
$(B)$ Cnidoblasts
$(C)$ Sensory cells
$(D)$ Germ cells