Final answer:
All the options presented (moistening food, changing food from large to small particles, and propelling food through the digestive tract) are part of mechanical digestion, therefore 'd. All of the above are examples of mechanical digestion' is correct.
Step-by-step explanation:
Mechanical digestion refers to the physical breakdown of food into smaller pieces, a key part of the digestive process. This process does not involve chemical change to the food's composition. Option 'a' indicates moistening the food, which is a prelude to mechanical digestion as it prepares the food to be broken down into smaller particles. Option 'b', changing food from large to small particles, is the essence of mechanical digestion and occurs through mastication or chewing in the mouth and continues with the churning actions in the stomach.
Finally, option 'c', propelling food through the digestive tract, refers to the movement of food which includes peristalsis—wave-like muscle contractions that push food through the digestive system, also a form of mechanical digestio. Therefore, the correct answer is 'd. All of the above are examples of mechanical digestion.'