Final answer:
The correct answer is C. The appendix, as it is not an accessory organ of the digestive system unlike the liver, gallbladder, and pancreas which secrete or store substances for digestion.
Step-by-step explanation:
The student's question seeks to identify which organ listed is not an accessory organ of the digestive system. The accessory organs of the digestive system include the liver, gallbladder, pancreas, salivary glands, teeth, and tongue. According to the reference information, the accessory organs secrete or store substances needed for digestion, but food does not pass through them. These organs significantly contribute to the breakdown of food into nutrients without directly being part of the gastrointestinal (GI) tract.
Among the options given to the student (A. Gallbladder, B. Pancreas, C. Appendix, D. Liver), the appendix stands out as the one that is not an accessory organ of the digestive system, as the appendix is part of the large intestine and does not contribute secretions for digestion. Therefore, the correct answer is C. The appendix.