Final answer:
Adding sugar to egg whites stabilizes the foam by interfering with the protein network, preventing it from becoming too tight and allowing the foam to hold its structure.
Step-by-step explanation:
The correct answer is c) It stabilizes the foam. When egg whites are beaten, they form a foam due to the proteins in the egg whites unfolding and creating a network of air bubbles. However, if they are overbeaten, the protein network becomes too tight and the foam collapses. Adding sugar to the egg whites stabilizes the foam by interfering with the protein network, preventing it from becoming too tight and allowing the foam to hold its structure.