Final answer:
Freshly-baked bread becomes light and fluffy due to the action of yeast on sugar, causing the dough to expand.
Step-by-step explanation:
Freshly-baked bread is light and fluffy as a result of the action of yeast on sugar. The yeast converts the sugar to carbon dioxide, which at high temperatures causes the dough to expand. The end result is an enjoyable treat, especially when covered with melted butter.