In general, more complex animals are
a) more likely to rely on chemical digestion than to rely on mechanical digestion.

b) more likely to perform intracellular digestion than extracellular digestion.

c) more likely to have one body opening that to have two body openings.

d) more likely to have a digestive tract than to have a gastrovascular cavity.

D) more likely to have a digestive tract than to have a gastrovascular cavity.

Explanation:

Complex animals are the organisms which have complex body types and tissue system so as to perform functions like respiration, circulation, digestion and excretion.

Among the options given, D) more likely to have a digestive tract than to have a gastrovascular cavity. is the correct one because of the fact that complex animals eat foods which contains carbohydrates, proteins and fats which are digested by the complex digestive system. The animal digestive system secretes digestive enzymes and juices by the gastric vascular cavity which helps in simplifying the food and facilitates it's digestion.