Acharacteristic of most mollusks is
a. an endoskeleton.
b. a two-part body plan.
c. the absence of a body cavity.
d. bilateral symmetry.

d. bilateral symmetry

Explanation:

Mollusks are the living things that have a soft tissue and they also have a hard cover, like snails.

They also are in the group of the invertebrates, that mean, that they do not have bones and of course back bone. So they do not have endoskeleton structure.

Also the mollusk have 3 body parts, the head, the foot, and the central ventral ( the one that cover the belly). So, they have 3 body parts, no 2.