If we do not clean our teeth and mouth after eating food, then many harmful micro-organisms called A begin to grow and live on the tooth. These micro-organisms act on the substance B present in the left-over food particles sticking to the tooth to form C. The C eats up the parts D and E of the tooth gradually and ultimately make a hole in the tooth. When this hole reaches part F of the tooth, our tooth becomes painful and we get toothache.
What is B?

Answer

**Step-by-Step Solution:**

1. **Understanding the Problem**: The question describes a process that occurs when we do not clean our teeth after eating. Harmful microorganisms grow on our teeth, and we need to identify the substance referred to as B.

2. **Identifying Microorganisms**: The harmful microorganisms that grow on our teeth are likely bacteria. These bacteria thrive on leftover food particles if we do not clean our teeth.

3. **Analyzing Substance B**: The transcript mentions that these microorganisms act on a substance present in the leftover food particles. The most common substance found in many foods, especially those we consume, is sugar.

4. **Formation of Substance C**: When bacteria consume sugar (substance B), they produce acid. This acid is what leads to the degradation of the tooth structure.

5. **Consequences of Tooth Decay**: The acid produced by the bacteria eats away at the tooth's enamel and dentine, leading to cavities (holes) in the tooth. When these cavities reach the pulp of the tooth, it results in pain, commonly known as a toothache.

6. **Conclusion**: Based on the analysis, the substance B that the microorganisms act upon is sugar.

**Final Answer**: B is sugar.

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