Sea hare is
A. Chiton
B. Nautilus
C. Aplysia
D. Cypraea

Hint: It belongs to a genus of medium to extremely large sea slugs, mainly Sea hares which is a single clade of large sea slugs, marines of molluscs gastropods. As compared with other molluscs these herbivorous benthic organisms may become large.

Complete answer:
-Chiton: These Chitons are marine molluscs of different sizes in the class Polyplacophora, and they were formerly known as Amphineura. Chitons are also known as sea cradles or coats of mail shells or occasionally known as polyplacophora.
-Nautilus: Nautilus is a pelagic marine mollusc of the class Cephalopoda in the family Nautilidae which is the only family remaining belonging to the Nautilaceae superfamily and also to its smaller but nearly equal suborder i.e. Nautilina.
-Aplysia: Aplysia is also known as the hare of the sea which is a large sea slug genus. They are marine gastropod molluscs which belong to the Aplysiidae family. They have parapodium which they used for swimming, breathing, and locomotion.
-Cypraea: It is a genus of medium to large-sized sea snails or cowries, marine gastropod molluscs that belong to the family Cypraeidae.

Hence, the correct answer is option (C).

Additional information: They feed in tropical coastal and subtidal areas, mainly in the Indo-Pacific Ocean but also found in the Atlantic Ocean.
-It is suspected that when attacked the Aplysia species release out clouds of ink to blind the attacker, while only very few species are considered edible.

Note: Aplysia is a large, shell-less marine snail that is best known to neuroscientists for its use in the understanding of the cellular and molecular basis of learning and memory.