Analysis: Microbial fermentation is of great significance in food production, such as steaming steamed bread, making bread, brewing beer, etc. Therefore, the answer is based on this. When making steamed bread or bread, yeast is often used, which can decompose glucose in flour and produce carbon dioxide. Carbon dioxide is a gas, which forms pores when it expands thermally, making steamed bread or bread soft and empty. It can be seen that C meets the question. Therefore, C Comments: Fermentation of microorganisms such as yeast is used in food production.