Hole D is the answer to this question. Hole D comes with Amylase and this is a type of enzyme that is in charge of exchanging the starch that we get from food into sugar. This type of substance can already be found in saliva which means that the moment that we eat something, the amylase will already start digesting the food that we eat.
This is also true for other mammals. Take note that Amylase can also be present in the blood but the amount should be just enough. There are certain conditions that can make the amylase that is found in the body higher than usual such as a pancreatic disorder.