Concept:Enzymes are biological catalysts that speed up chemical reactions in living organisms.Explanation:Brewing of beer depends on fermentation carried out by yeast.Yeast produces enzymes that convert sugars into alcohol and carbon dioxide.The other processes do not use enzymes.Liquefaction of air is a physical separation process.Manufacture of soap involves saponification using an alkali.Catalytic cracking uses inorganic catalysts, not enzymes.Answer:C. Brewing of beer