[A]: lmmunoglobulins or antibodies are specilialized proteins synthesized by the lym- phocytes of vertebrates.
[R]: These defend against invasion of bacte- ria, viruses and foreign proteins.

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Immunoglobulins or antibodies are specialized proteins synthesized by the lymphocytes of vertebrates."
- **Explanation**: Immunoglobulins (antibodies) are indeed specialized proteins produced by a type of white blood cell known as lymphocytes, specifically B-cells. This statement is true.

2. **Understanding the Reason**: The reason states that "These defend against invasion of bacteria, viruses, and foreign proteins."
- **Explanation**: Antibodies play a crucial role in the immune response by identifying and neutralizing pathogens such as bacteria and viruses. This statement is also true.

3. **Analyzing the Relationship**: Now we need to determine if the reason is the correct explanation for the assertion.
- **Explanation**: The reason explains the function of antibodies, which directly relates to their synthesis by lymphocytes. Therefore, the reason is indeed a correct explanation for the assertion.

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

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

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