Analysis of test questions: When making steamed bread or bread, yeast is often used. Yeast can decompose glucose in flour and produce carbon dioxide. Carbon dioxide is a gas, which will form pores when it expands, making steamed bread or bread soft and empty. During this period, an alkaline solution is usually added to the fermented dough. According to the principle of acid-base neutralization, soda solution can neutralize and remove the acid produced during fermentation, and carbon dioxide gas will be produced in the process of acid-base neutralization, which will expand the volume of steamed bread. Choose C.