Given below are two statements, one labeled as Assertion (A) and the other labeled as Reason (R). **Assertion (A):** Tooth decay starts when the pH of the mouth is lower than 5.5. **Reason (R):** Tooth enamel, made of calcium phosphate (hydroxyapatite), is the hardest substance in the body and dissolves easily in pure water. Select the correct answer using the codes given below:

Options:

• A: Both A and R are true and R is the correct explanation of A
• B: Both A and R are true but R is not the correct explanation of A
• C: A is true but R is false
• D: A is false but R is true

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