Some washing powders include enzymes together with detergent. In an experiment, three pieces of cloth were each stained with the same material. They were placed in separate beakers containing detergent, with enzyme added to some of them, at $40\,^{\circ}\text{C}$ for 30 minutes. Which statement is correct for the results shown by this experiment?
- AThe black stain contained carbohydrate.
- BThe black stain contained fat.
- CThe black stain contained protein.
- DThe black stain contained water.