Adenosine is `:`

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding Adenosine**:
- Adenosine is a compound that is part of our genetic material. It is important to identify its components and classification.

2. **Components of Genetic Material**:
- Genetic material, such as DNA, is made up of three main components:
- A nitrogenous base
- A sugar molecule
- A phosphate group
- When these three components come together, they form a nucleotide.

3. **Distinguishing Between Nucleotide and Nucleoside**:
- If we consider only the sugar and nitrogenous base (without the phosphate group), this combination is referred to as a nucleoside.
- Therefore, adenosine, which consists of adenine (a nitrogenous base) and a sugar (ribose), is classified as a nucleoside.

4. **Classification of Nitrogenous Bases**:
- Nitrogenous bases are categorized into two groups: purines and pyrimidines.
- Purines include adenine and guanine.
- Pyrimidines include thymine, cytosine, and uracil.

5. **Identifying Adenosine**:
- Since adenosine is derived from adenine (which is a purine), and it is a nucleoside (sugar + nitrogenous base), we conclude that adenosine is a purine nucleoside.

6. **Final Answer**:
- Therefore, the answer to the question "Adenosine is:" is that adenosine is a purine nucleoside.

---