Thick layers of muscles are present on the walls of the alimentary canal.
These muscles are part of the muscularis layer of the intestine. It helps control the movement of the intestine called peristaltic movement.
The action of muscles helps with the peristaltic movement of the intestine.
As the muscle contracts and relaxes, the food material gets mixed with the enzymes present in the intestine. These enzymes are secreted by the different glands in the alimentary canal.
This helps with the proper digestion of food in the intestine.
Therefore both the assertion and the reason are true and the reason is the perfect explanation for the assertion.
Hence, the correct answer is option (A).