Read the following text and answer the question on the basis of the same:
DNA, a long polymer of deoxyribonucleotide. Altmann and these substances to be acidic hence he named nucleic acid. The basic unit of DNA is a nucleotide which has three components a nitrogenous base, a pentose sugar (deoxyribose) and a phosphate group. There are two types of nitrogenous bases in DNA, Purine and Pyrimidine. J. Watson and E. Crick proposed a double helix model for the structure of DNA. There are four types of DNA i.e., A, B, C, Z.
Cytidine is a:

Options

A. Nucleoside
B. Nitrogen base
C. Nucleotide
D. Common dinucleotide in DNA and RNA.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about "Cytidine" in the context of the provided text about DNA and its components.

2. **Identifying Components of DNA**: From the text, we know that DNA is made up of nucleotides, which consist of three components: a nitrogenous base, a pentose sugar (deoxyribose), and a phosphate group.

3. **Defining Cytidine**: Cytidine is a specific type of nucleoside. A nucleoside is formed when a nitrogenous base (in this case, cytosine) is attached to a pentose sugar (ribose or deoxyribose) without a phosphate group.

4. **Differentiating between Nucleotide and Nucleoside**: The key difference is that a nucleotide contains a phosphate group, while a nucleoside does not. Since cytidine lacks a phosphate group, it is classified as a nucleoside.

5. **Conclusion**: Therefore, the correct classification of cytidine is that it is a nucleoside.

**Final Answer**: Cytidine is a nucleoside.

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