[A]: Treatment of malaria by vaccination is out of question.
[R]: Plasmodium does not produce antibod- ies in human blood.

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 (A)**: The assertion states that "treatment of malaria by vaccination is out of question." This implies that vaccination is not a viable method for treating malaria.

2. **Understanding the Reason (R)**: The reason provided is that "Plasmodium does not produce antibodies in human blood." This suggests that the malaria-causing parasite, Plasmodium, does not elicit an immune response that would be necessary for a vaccine to be effective.

3. **Explaining Malaria and its Pathogen**: Malaria is caused by the Plasmodium parasite, which has several species, including Plasmodium vivax and Plasmodium falciparum. The disease is transmitted through the bite of infected female Anopheles mosquitoes.

4. **Mechanism of Infection**: When an infected mosquito bites a human, the Plasmodium enters the bloodstream and travels to the liver, where it multiplies. After this, it infects red blood cells (RBCs), leading to their rupture and the release of a toxic substance called haemozoin, which causes the characteristic symptoms of malaria, such as fever.

5. **Vaccination and Immune Response**: Vaccination works by introducing an antigen that stimulates the immune system to produce antibodies. However, in the case of malaria, the Plasmodium parasite ruptures the RBCs and does not produce antibodies in the human body. Therefore, the immune system does not have a target to create an effective immune response through vaccination.

6. **Conclusion**: Since vaccination relies on the ability of the immune system to produce antibodies against a pathogen, and since Plasmodium does not produce antibodies, the assertion that "treatment of malaria by vaccination is out of question" is true. The reason that "Plasmodium does not produce antibodies in human blood" is also true. Therefore, both the assertion and the reason are true, and the reason correctly explains the assertion.

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

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