Which of the following is a nucleoside

Options

A. Adenosine, Adenylic acid, Cytosine
B. Adenosine, Guanosine, Cytidine
C. Cytidylic acid, adenosine, Adenylic acid
D. Guanylic acid, Cytosine, Adenosine

Answer

To determine which of the following is a nucleoside, we need to understand the definition and components of a nucleoside.

### Step-by-Step Solution:

1. **Understanding Nucleosides**: A nucleoside is a molecular structure that consists of a nitrogenous base attached to a sugar molecule (either ribose or deoxyribose). Importantly, it does not contain a phosphate group.

2. **Identifying Components**: The nitrogenous bases can be classified into two categories:
- **Purines**: Adenine (A) and Guanine (G)
- **Pyrimidines**: Cytosine (C), Thymine (T), and Uracil (U)

3. **Formation of Nucleosides**: When a nitrogenous base attaches to a sugar (ribose for RNA or deoxyribose for DNA), it forms a nucleoside:
- Adenine + Ribose = Adenosine
- Guanine + Ribose = Guanosine
- Cytosine + Ribose = Cytidine
- Uracil + Ribose = Uridine

4. **Analyzing the Options**:
- If the options include "adenosine," "guanosine," "cytidine," or "uridine," these would be nucleosides.
- If the options include "cytosine," "adenylic acid," "cytidylic acid," or "guanylic acid," these are not nucleosides but rather nitrogen bases or nucleotides.

5. **Selecting the Correct Answer**: Based on the definitions and the analysis of the options, the correct answer is the one that represents a nucleoside.

### Conclusion:
The correct answer is **option number two**, which is a nucleoside.