The correct answer is: C. Small intestine
The small intestine is the longest part of the digestive system, and it is where most digestion and absorption of nutrients takes place. The small intestine is about 20 feet long and is divided into three parts: the duodenum, jejunum, and ileum.
The duodenum is the first part of the small intestine, and it is where the stomach contents are mixed with bile and pancreatic juices. Bile is a fluid that helps to break down fats, and pancreatic juices contain enzymes that help to break down carbohydrates, proteins, and fats.
The jejunum is the middle part of the small intestine, and it is where most of the nutrients are absorbed. The jejunum has a large surface area, which is important for absorption. The jejunum also has many villi, which are small finger-like projections that increase the surface area even more.
The ileum is the last part of the small intestine, and it is where bile salts and vitamin B12 are absorbed. The ileum also has a large surface area, but it does not have as many villi as the jejunum.
The small intestine is a very important part of the digestive system, and it is where most digestion and absorption of nutrients takes place.