A: Incomplete dominance!
Incomplete dominance is when a dominant allele doesn’t completely mask the effects of the other. The organism, as a result, will show a blending of both.
The answer is single opening. The gastrovascular cavity varies from the alimentary canal in that only the gastrovascular cavity has only a single opening. In addition, an alimentary canal has two openings and food moves over it unidirectional. The gastrovascular cavity is a construction establish in primitive animal phyla. It is accountable in cooperation with the digestion of food and the transportation of nutrients all over the body.