Which of the following is the longest part of the alimentary canal?

The small intestine is the alimentary canal's longest segment. It is usually 6 to 7 metres long and coiled inside the abdominal cavity. 

The small intestine is in charge of most nutrient absorption in the digestive system. It is lined with numerous finger-like projections called villi, which increase the intestine's surface area and allow for more efficient nutrient absorption from digested food. 

The small intestine also receives pancreatic and liver secretions, which contain digestive enzymes that aid in the breakdown of food. 

Nutrients from food are absorbed into the bloodstream through the walls of the small intestine after food has been partially digested there.