The correct answer is the mouth. Digestion begins when food enters the mouth, chewed, and mixed with saliva. Food usually has complex carbohydrates such as starch in them and saliva has an enzyme called salivary amylase which can break down these complex carbohydrates into simpler molecules (i.e. dextrins). After which, these dextrins are digested further in the stomach and in the small intestine by the action of enzymes such as the pancreatic amylase which further breaks down dextrins into oligosaccharides and disaccharides. Other enzymes such as trypsin breaks down proteins into amino acids and lipase that breaks down fat into triglycerides. In the brush border of the small intestine, there are enzymes such as oligosaccharidases and disaccharidases which breaks down sugars into their most basic forms (i.e. glucose, fructose, galactose) which can be readily absorbed in the intestine. Amino acids and tricglycerides are also readilty absorbed in the intestines with the latter by the help of emulsification by bile.
