Final answer:
Both the saliva breaking down a piece of bread and the browning of avocado are examples of chemical changes.
Step-by-step explanation:
Both the saliva breaking down a piece of bread and a piece of avocado turning brown are examples of chemical changes.
Saliva contains enzymes that break down the starches in bread into simpler sugars, which is a chemical change. The browning of avocado occurs due to the oxidation of certain compounds in the avocado, which is also a chemical change.
Therefore, options c) Both are chemical changes apply to both scenarios.