An advantage of a complete digestive system over a gastrovascular cavity is that the complete system

Here is the complete sentence: An advantage of a is that the complete system HAVE SPECIALIZED REGIONS THAT PERFORM SPECIALIZED FUNCTIONS.

Explanation:

The digestive system is a set of organs that work together to break down food molecules into the forms that the body cells can absorb and use. The gastrovascular cavity is an organ of digestion and circulation in some primitive living organisms. Gastrovascular cavity is an unspeciallized organ with two openings, one of the opening is the mouth while the other one is the anus, through which wastes pass out of the body.

The major advantage of complete digestive system over gastrovascular cavity is that the digestive system comprise of specialized organs which perform specialized functions. For instance, the stomach is a specialized organ that is responsible for churning of food during digestion, it also perform other specialized functions.