Answer :
The mouth, oesophagus, stomach and intestines help to form an organ system called the digestive system. So the correct option is D.
What is the digestive system?
The digestive system is formed from a long tube which begins at the mouth and goes down to the anus. It is also called the alimentary canal as it is a single long tune that forms all of these organs.
The digestive system performs the function of breakdown of food into its constituent nutrients and the absorption of the nutrients into the blood.
The process of digestion begins at the mouth by the saliva and a bolus is formed. This goes down through the oesophagus by muscular movements called the peristaltic movements. These movements continuously push the food down.
The bolus reaches the stomach where it is further broken down into a semisolid consistency called chyme. This moves to the small intestine where the final breakdown and absorption take place.
Undigested food and water moves to the large intestine. Undigested food forms the faeces which are expelled through the anus and water is absorbed in the large intestine.
Therefore the correct option D.
Read more about the digestive system, here
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