Fill in the blanks
The …..a……. Lymphoid organs provide the sites for interaction of lymphocytes with antigen which then proliferate to become …..b…..
2 . The thymus is a lobed organ located near the heart and beneath the ….C…..
3. Spleen has a large reservoir of .....d.....

Options

A. a- primary, b—antigen sensitive cells, c-collar bone,d- lymphocytes
B. a-secondary, b-receptor cells, c-breast bone,d- erythrocytes
C. a-primary, b-effector cells, c-breast bone, d-lymphocytes
D. a-secondary , b-effector cells, c-breast bone, d-erythrocytes

Answer

### Step-by-Step Text Solution:

1. **Identify the Types of Lymphoid Organs**:
- There are two types of lymphoid organs: primary and secondary.
- Primary lymphoid organs include the bone marrow and thymus, while secondary lymphoid organs include the spleen and tonsils.

2. **Fill in the First Blank (a)**:
- The question asks for the type of lymphoid organs that provide sites for interaction of lymphocytes with antigens.
- The correct answer is "secondary" lymphoid organs.
- Therefore, the first blank (a) is filled with "secondary".

3. **Fill in the Second Blank (b)**:
- After lymphocytes interact with antigens, they proliferate to become effector cells.
- The correct term to fill in the second blank (b) is "effector cells".

4. **Fill in the Third Blank (c)**:
- The thymus is located near the heart and beneath the breastbone, which is also known as the sternum.
- Therefore, the third blank (c) is filled with "sternum".

5. **Fill in the Fourth Blank (d)**:
- The spleen has a large reservoir of red blood cells, which are also referred to as erythrocytes.
- Thus, the fourth blank (d) is filled with "erythrocytes".

### Final Answers:
1. a: secondary
2. b: effector cells
3. c: sternum
4. d: erythrocytes

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