Adenosine is `:`

Options

A. nucleoside
B. nucleotide
C. a purine
D. a pyrimdine

Answer

To determine what adenosine is, we can follow these steps:

### Step 1: Understand the Basic Definitions
- **Nucleotide**: A nucleotide is a building block of nucleic acids, consisting of a nitrogenous base, a sugar (ribose or deoxyribose), and a phosphate group.
- **Nucleoside**: A nucleoside consists of a nitrogenous base and a sugar, but it does not contain a phosphate group.
- **Purine and Pyrimidine**: These are two categories of nitrogenous bases. Purines include adenine and guanine, while pyrimidines include cytosine, thymine, and uracil.

### Step 2: Identify the Components of Adenosine
- Adenosine is derived from adenine, which is a purine base.
- Adenosine consists of adenine attached to a ribose sugar.

### Step 3: Classify Adenosine
- Since adenosine is made up of a nitrogenous base (adenine) and a sugar (ribose), but lacks a phosphate group, it fits the definition of a nucleoside.

### Step 4: Conclusion
- Therefore, adenosine is classified as a **nucleoside**.

### Final Answer
Adenosine is a **nucleoside**.

---