How do we come to know that food is spoiled?

Spoiling refers to the degradation of food items. Food usually gets spoiled within two-three days. It is advised that one should consume spoiled. It affects our health and can make us very sick by causing food poisoning. Spoilt food is characterized by its smell, taste and appearance. It has a foul smell. It tastes sour or different from the usual taste. It appears softer than normal due to the action of various bacteria and fungi. 

Therefore, the correct answer is (D).