A: Yellow bone marrow is reserve erythropoietic tissue.
R: After severe bleeding yellow marrow may convert to red marrow.

Options

A. Inner lining of savivary ducts - ciliated epithelium
B. Moist surface of buccal cavity - Glandular epithelium
C. Tubular parts of nephrons - Cuboidal epithelium
D. Inner surface of bronchioles - Squamous epithelium

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "Yellow bone marrow is reserve erythropoietic tissue."
- **Explanation**: Yellow bone marrow primarily serves as a storage area for fats but can also act as a reserve for erythropoiesis (the production of red blood cells) when needed.

2. **Evaluating the Reason (R)**:
- The reason states that "After severe bleeding, yellow marrow may convert to red marrow."
- **Explanation**: In situations of significant blood loss, the body requires an increased production of blood cells. To meet this demand, yellow bone marrow can convert into red bone marrow, which is responsible for producing red blood cells, platelets, and some white blood cells.

3. **Determining the Truth of the Statements**:
- Both the assertion and reason are true statements.
- The assertion correctly identifies the role of yellow bone marrow as a reserve for erythropoiesis.
- The reason accurately explains how yellow marrow can convert to red marrow in response to the body's needs after severe bleeding.

4. **Conclusion**:
- Since both statements are true and the reason correctly explains the assertion, the answer to the question is that both A and R are true, and R is the correct explanation of A.

### Final Answer:
Both the assertion (A) and reason (R) are true, and R correctly explains A.

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