Mixture should be the answer.
The digestion of the food in humans begins in the mouth. In the mouth, the salivary amylase enzyme digests and breaks down a small amount of the starch present in the food. The digestion process begins right in the mouth. and continues till the intestine. The carbohydrates (starch) are the ones whose digestion starts in the mouth.
Hence, the blanks can be filled with 'mouth and amylase' respectively.
They both involve topics related to the natural world, and are both based on empirical evidence. <span />
