Question

jellyfish and coral are closely related. Which statement explains why we can say this?

Answer 1

Both are Cnidarians:

Both jellyfish and coral are Cnidaria (this, by the way, is the right spelling). They occupy different classes of the same phylum - therefore, by definition, they share the same overall body plan and a relatively recent common ancestor.
Note that the common ancestor between the two was *not* coral. Coral is a crown-group term and refers only to extant organisms. The common ancestor might've looked more like a sponge/coral than a jellyfish - it was probably sessile, affixed to the sea floor and capable of filter-feeding.