Assertion : The arrangement of axonemal microtubules in cilia or flagella is called 9 + 2 array.
Reason : The axoneme usually has nine pairs or doubles of radially arranged peripheral microtubules, and a pair of centrally located microtubules.

Options

A. If both assertion and reason are true amnd reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that the arrangement of axonemal microtubules in cilia or flagella is referred to as a "9 + 2 array." This means that there are nine outer pairs of microtubules and two central microtubules.

2. **Understanding the Reason**: The reason provided explains that the axoneme consists of nine pairs of radially arranged peripheral microtubules and a pair of centrally located microtubules. This description aligns with the definition of the 9 + 2 arrangement.

3. **Analyzing the Relationship**: The assertion and the reason are both true. The reason accurately describes the structure of the axoneme, which supports the assertion that it is called a "9 + 2 array."

4. **Conclusion**: Since both the assertion and reason are true, and the reason is the correct explanation of the assertion, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

### Final Answer:
**Option A**: Both assertion and reason are true, and reason is the correct explanation of the assertion.

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