Answer : Option D) Complete.
Explanation : In a complete digestive system, digestion takes place outside of the cells in a series of tubes. Food enters through one opening and food remnants exit out of a different opening. It has examples of humans, dogs, horses, spiders and earthworms. This system is complete because it does not occurs inside a cell nor it occurs in sponge kind-off organs and it is also not incomplete digestion as the waste products are removed from the other opening.
Therefore, the correct answer is option D) complete.