Question

what do scientists use to classify cnidarians into different classes within the phylum? their level of intelligence their habitat and diet their size and color their body shape and life cycle (polyp or medusa form)

Explanation:

Cnidarians are classified based on their body form (polyp or medusa) and life cycle. Intelligence level is not a factor as they are simple organisms. Habitat/diet and size/color are not primary classification criteria compared to body - shape and life - cycle characteristics.

Answer:

Their body shape and life cycle (polyp or medusa form)