A、Because they are unable to be read after the flood. B、Because they may contain dirt and germs from the flood water. C、Because

Food that has come in contact with flood water can sicken anyone who eats it. Water from floods may contain animal and human waste. It can also contain other pollutants like chemicals from agriculture and industry.
    Food safety experts suggest that anything that is not stored in a waterproof container should be thrown away if there is a chance of contact after a flood. Boxes of juice, milk or baby formula should also be thrown away if they have come into contact with flood water. (29) Damaged metal cans should be discarded. Cans that are swollen or leaking,or that are rusted or crushed,should not be used any more.
    But food safety experts also say that some unopened, undamaged all-metal cans can be saved. (30) First, remove any labels. The paper may contain dirt and germs from the floodwater. Wash the cans with soap and water,and brush or wipe away dirt. Use hot water and water that is safe for drinking if they are available. Next,place the cans again in water and heat the water to 100 degrees Celsius. Boil the cans for two minutes.
    Another way to disinfect the cans is in a freshly made solution of bleach. Use eight drops of liquid bleach for every four liters of water. (31) Use drinking water or the cleanest, clearest water available. Place the cans in the solution for 15 minutes.
    Let cleaned cans air-dry for at least one hour before opening or storing them. And relabel the cans with a marking pen to list their contents and any dates when the foods are best used by. Experts advise using the cans as soon as possible.
29. What do food safety experts suggest after flood?
30. Why should the labels on saved cans be removed?
31. What do we know about the second way of disinfecting the cans?