Food contaminants refer to any substances that are not intentionally added to food, but are brought into food during production, manufacturing, processing, preparation, processing, filling, packaging, transportation, and storage, or are brought into food due to environmental pollution. (ABC are intentionally joining). According to the above definitions, which of the following is food contaminants? ['"Problem Milk Powder" in "Sanlu Milk Powder" Incident Contains Melamine.', 'Water-melon protease ingredients used for tenderizing and improving meat quality.', 'Aluminum content due to the addition of increasing agents during processing of fried foods.', 'Nitrite that is harmful to the human body in additives used in food curing.']