Which of the following are purine bases?

Options

A. Guanine
B. Adenine
C. Thymine
D. Uracil

Explanation

To determine which of the given options are purine bases, we can follow these steps:

### Step 1: Understand the Types of Nitrogenous Bases
Nitrogenous bases are categorized into two main types: purines and pyrimidines.

**Hint:** Remember that purines have a two-ring structure, while pyrimidines have a single-ring structure.

### Step 2: Identify Purine Bases
The two purine bases are:
- Adenine (A)
- Guanine (G)

**Hint:** Recall that purines are characterized by their double-ring structure.

### Step 3: Identify Pyrimidine Bases
The pyrimidine bases include:
- Thymine (T)
- Uracil (U)

**Hint:** Pyrimidines can be remembered as having a single ring, which distinguishes them from purines.

### Step 4: Analyze the Given Options
Now let's look at the options provided:
1. Guanine
2. Adenine
3. Thymine
4. Uracil

From our previous identification:
- Guanine and Adenine are purine bases.
- Thymine and Uracil are pyrimidine bases.

**Hint:** Cross-reference the options with the definitions of purines and pyrimidines.

### Conclusion
The purine bases from the given options are:
- **Adenine**
- **Guanine**

**Final Answer:** Adenine and Guanine are the purine bases.