Complete the following paragraph by selecting the correct option for the blanks A,B and C.
The thymus gland is located between the lungs behind the sternum on the ......A.... Side of the aorta. .....B..... Secreted by the gland plays a major role in the differentiation of T- lymphocytes which provide ......C...... They also promote antibody production which provides.....D....
(a) A: dorsal , B : Thymic humoral factor , C : humoral immunity , D : Cell - mediated immunity
(b) A: Ventral , B : Thymopoietin , C: humoral immunity , D : cell - mediated immunity
(c) A: Ventral , B : Thymopoietin , C: humoral immunity , D : cell - mediated immunity
(d) A: Ventral , B : Thymosin , C: cell - mediated , D : humoral immunity

Options

A. A: dorsal , B : Thymic humoral factor , C : humoral immunity , D : Cell - mediated immunity
B. A: Ventral , B : Thymopoietin , C: humoral immunity , D : cell - mediated immunity
C. A: Ventral , B : Thymopoietin , C: humoral immunity , D : cell - mediated immunity
D. A: Ventral , B : Thymosin , C: cell - mediated , D : humoral immunity

Answer

To complete the paragraph regarding the thymus gland, we will analyze each blank step by step.

### Step-by-Step Solution:

1. **Blank A**: The thymus gland is located between the lungs behind the sternum on the ......A.... Side of the aorta.
- The thymus is situated in the anterior (ventral) part of the thoracic cavity, specifically between the lungs and behind the sternum. Therefore, the correct answer for Blank A is "ventral."

2. **Blank B**: .....B..... Secreted by the gland plays a major role in the differentiation of T- lymphocytes which provide ......C......
- The thymus gland secretes several hormones that are crucial for the maturation and differentiation of T-lymphocytes. One of the primary hormones is "thymosin." Thus, the correct answer for Blank B is "thymosin."

3. **Blank C**: They provide ......C......
- T-lymphocytes are primarily involved in "cell-mediated immunity." This type of immunity is characterized by the direct action of T-cells against infected or cancerous cells. Therefore, the correct answer for Blank C is "cell-mediated immunity."

4. **Blank D**: They also promote antibody production which provides.....D....
- While T-lymphocytes do not produce antibodies directly, they assist B-lymphocytes in producing antibodies, which is a key aspect of "humoral immunity." Therefore, the correct answer for Blank D is "humoral immunity."

### Final Completed Paragraph:
The thymus gland is located between the lungs behind the sternum on the **ventral** side of the aorta. **Thymosin** secreted by the gland plays a major role in the differentiation of T-lymphocytes which provide **cell-mediated immunity**. They also promote antibody production which provides **humoral immunity**.

### Selected Option:
The correct option is (d): A: Ventral, B: Thymosin, C: Cell-mediated immunity, D: Humoral immunity.