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

Options

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

Explanation

To solve 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 1: Identify the Type of Virus
In some viruses, particularly retroviruses, DNA is synthesized from RNA. A well-known example of a retrovirus is the Human Immunodeficiency Virus (HIV).

**Hint:** Think about viruses that use RNA as their genetic material.

### Step 2: Understand the Process
The process by which DNA is synthesized from an RNA template is known as reverse transcription. This is the opposite of the usual transcription process, where DNA is transcribed into RNA.

**Hint:** Consider the term "reverse" in the context of transcription.

### Step 3: Identify the Enzyme Involved
The enzyme responsible for this process is called reverse transcriptase. This enzyme catalyzes the conversion of RNA into complementary DNA (cDNA).

**Hint:** Remember that enzymes often have names that reflect their function.

### Step 4: Define the Resulting DNA
The DNA synthesized from an RNA template is referred to as complementary DNA, or cDNA. This term highlights that it is complementary to the RNA strand used as a template.

**Hint:** Look for terms that indicate the relationship between the original RNA and the newly formed DNA.

### Conclusion
Thus, the answer to the question is that the DNA synthesized from RNA in some viruses is called **cDNA (complementary DNA)**.

**Final Answer:** cDNA (complementary DNA)