A Recent Study of the Marine Hawksbill Turtle's Stomach Contents

A recent study of the marine hawksbill turtle's stomach contents revealed that sponges constitute a major portion of their diet.Sponge beds are generally protected from predators by the sponge's calcium and silica crystals,but these were found in quantity in the turtles' digestive systems.These structures that protect the sponges from most predators,but not turtles,are

A) amoebocytes.
B) the osculum.
C) choanocytes.
D) spicules.
E) spongin.