Consider the following statement regarding humans.
a. Duodenum is the longest part of the small intestine.
b. Hepatic and cystic ducts release their secretions into the common bile duct whose opening is controlled by the sphincter of Oddi.
c. Ileocaecal valve is present at the junction of small intestine and large intestine
d. Mechanical digestion and chemical digestion of food occurs in buccal cavity, stomach and small intestine.
Which of the following choices is correct?

A. a and b only
B. b and c only
C. c and d only
D. a, b, c and d

Hint: Digestion associated with the breakdown of food into tiny or absorbable components, so they can be consumed and incorporated into the body. As food transfers via the GI tract, it blends with digestive juices, resulting in huge molecules of food to break down into tiny particles.

Complete Answer:
To answer this question, first, we need to know about the human digestive system. The human digestive system contains primarily the digestive tract, or the series of structures and organs through which food and liquids pass during their processing into forms absorbable into the bloodstream.

The digestive tract starts at the tops and ends at the anus. It includes the mouth, or oral cavity, with its teeth, for grinding the food, and its tongue, which serves to knead food and mix it with saliva; the throat, or pharynx; the esophagus; the stomach; the small intestine, consisting of the duodenum, the jejunum, and the ileum; and the large intestine, consisting of the cecum, a closed-end sac connecting with the ileum, the ascending colon, the transverse colon, the descending colon, and the sigmoid colon, which terminates in the rectum.

Now, let us find the solution from the option.
- Ileum is the longest part of the small intestine.
- Bile duct and pancreatic duct unblock together into the duodenum as usual hepato-pancreatic duct that is protected by a sphincter known as the sphincter of oddi.
- Ileocaecal valve is present at the junction of small intestine and large intestine.
- Mechanical digestion and chemical digestion of food occurs in buccal cavity, stomach and small intestine.

Thus, the correct option is D. i.e. a, b, c and d.

Note: The phenomenon of digestion has three phases. The first phase is the cephalic phase of digestion which starts with gastric eliminations as a result of the sight and smell of food. This stage involves the mechanical digestion of food by chewing, and the chemical malfunction by digestive enzymes that occur in the mouth.