Assertion : Muscle cells are also called myofibrils.
Reason : Muscle cells are very thin and elongated.

Options

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

Explanation

To analyze the assertion and reason provided in the question, we can break it down step by step:

### Step 1: Understanding the Assertion
The assertion states that "Muscle cells are also called myofibrils."
- **Explanation**: Muscle cells are known as myocytes, not myofibrils. Myofibrils are actually the contractile units within muscle cells. Therefore, this assertion is incorrect.

### Step 2: Understanding the Reason
The reason states that "Muscle cells are very thin and elongated."
- **Explanation**: This statement is true. Muscle cells (myocytes) are indeed thin and elongated, which allows them to contract effectively and facilitate movement.

### Step 3: Conclusion
Based on the analysis:
- The assertion is false because muscle cells are not called myofibrils; they are called myocytes.
- The reason is true because muscle cells are thin and elongated.

### Final Answer
The correct conclusion is that the assertion is false, but the reason is true.