In some viruses, DNA is synthesized by using RNA as template. Such a DNA is called

Options

A. A-DNA
B. B-DNA
C. cDNA
D. rDNA

Explanation

To answer the question, "In some viruses, DNA is synthesized by using RNA as a template. Such a DNA is called," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about a specific type of DNA that is synthesized from an RNA template in certain viruses.

2. **Identifying the Key Terms**: The key terms in the question are "DNA," "synthesized," "RNA," and "template." This indicates that we are looking for a process where RNA serves as a template for DNA synthesis.

3. **Recalling Relevant Concepts**: In molecular biology, there is a process known as reverse transcription. This process is where RNA is used as a template to synthesize DNA.

4. **Identifying the Enzyme**: The enzyme responsible for this process in certain viruses, such as retroviruses, is called reverse transcriptase. This enzyme catalyzes the conversion of RNA into complementary DNA (cDNA).

5. **Defining cDNA**: The DNA synthesized from an RNA template is referred to as complementary DNA or cDNA. This term is specifically used to describe the DNA that is synthesized in this manner.

6. **Choosing the Correct Answer**: Based on the above steps, the correct answer to the question is cDNA.

### Final Answer:
The DNA synthesized by using RNA as a template in some viruses is called **cDNA**.

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