Flatworms are similar to cnidarians in that both flatworms are similar to cnidarians in that both are chordates exhibit bilateral symmetry have true tissues lack a gastrovascular cavity

The correct answer is that flatworms are similar to cnidarians in that both have true tissues. 

Flatworms and cnidarians are not chordates as they are invertebrates. Only flatworms exhibit bilateral symmetry and only cnidarians lack a gastrovascular cavity. Both of which, though, have true tissues.