The vertebrate digestive system consists of a two-way tube with
A. a separate mouth and anus and accessory organs.
B. a one-way tube with a separate mouth and anus and accessory organs.
C. a two-way tube with a separate mouth and anus.
D. a tube with a single opening that serves as mouth and anus.
E. a one-way tube with a separate mouth and anus and no accessory organs.