[A]: Vectors carry the foreign DNA/gene into the host cell.
[R]: Plasmids can carry recombinant DNA but viruses can not.

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 vectors carry foreign DNA or genes into host cells.
- **Explanation**: In molecular biology, vectors are vehicles used to transfer genetic material into a host cell. Common examples of vectors include plasmids and viruses.

2. **Evaluating the Assertion**: The assertion is true because vectors, such as plasmids and viruses, are indeed used to introduce foreign DNA into host cells for various applications, including cloning and gene therapy.

3. **Understanding the Reason (R)**: The reason states that plasmids can carry recombinant DNA but viruses cannot.
- **Explanation**: Plasmids are circular DNA molecules that can be engineered to carry foreign DNA and replicate within bacterial cells. However, viruses can also be modified to carry recombinant DNA and deliver it into host cells.

4. **Evaluating the Reason**: The reason is false because both plasmids and viruses can serve as vectors to carry recombinant DNA. While plasmids are commonly used, certain viruses (like retroviruses) are also capable of carrying and delivering recombinant DNA.

5. **Conclusion**: Since the assertion is true and the reason is false, the correct answer is that A is true and R is false.

### Final Answer:
- The correct option is: **A is true and R is false.**

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