Chordates have a complete digestive system and a closed circulatory system.
Because reptiles are vertebrates, they are chordates.
Reptiles have a complete digestive system and a closed circulatory system.
What have a complete digestive system and a closed circulatory system?

[a] viruses
[b] reptiles
[c] phytoplankton
[d] mammals
[e] bacteria
[f] graptolites
[g] humans
[h] elephants