Which action is a physical change in digestion?

producing enzymes for nutrient absorption
absorbing nutrients from food
mashing food with teeth
salivating to break food into carbohydrates

mashing food with teeth

A physical change alters the physical structure of a matter. The shape and size of matter may change in this process, but no chemical change occurs. These changes are generally reversible. Mashing or mastication of food is the process in which food is crushed or grinded by teeth. This process brings a physical change in the food, but it's chemical composition remains the same.  

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