Final answer:
Cheese stimulates saliva flow and helps balance the pH in the mouth with its buffer action, which neutralizes acids and protects teeth from decay.
Step-by-step explanation:
Among the options provided, cheese is the food that stimulates saliva flow and neutralizes acids in the mouth. Saliva contains bicarbonate and phosphate ions that function as chemical buffers, maintaining a pH that's close to neutral. When saliva mixes with food, it starts the digestive process by breaking down carbohydrates with the enzyme salivary amylase and lubricating the food with mucus for easier swallowing. Cheese has the effect of increasing saliva flow, which helps rinse the mouth and balance out the acidic environment, therefore protecting teeth from decay. Other options such as hamburger and orange juice do not have this neutralizing effect, and in fact, orange juice due to its acidity might contribute to a lower pH in the mouth. On the other hand, legumes, though healthy, are not specifically known for stimulating saliva flow and neutralizing mouth acids.