Connecting link.

Options

A. 1)link between two classes
B. 2)link between two groups
C. 3)link between two kingdoms
D. 4)all of the above

Answer

### Step-by-Step Solution:

1. **Understanding the Concept of Connecting Link**:
- A connecting link refers to an organism that exhibits characteristics of two different groups or categories of organisms. This concept is crucial in understanding evolutionary biology and the relationships between different species.

2. **Identifying the Options**:
- The question provides four options regarding what a connecting link represents:
1. Link between two classes
2. Link between two groups
3. Link between two kingdoms
4. All of the above

3. **Analyzing the Options**:
- **Option 1**: Link between two classes – This is too specific and does not encompass the broader idea of connecting links.
- **Option 2**: Link between two groups – This is a more accurate description, as connecting links can exist between various groups of organisms.
- **Option 3**: Link between two kingdoms – While some connecting links may exist between kingdoms, this option is also too specific.
- **Option 4**: All of the above – Since options 1, 3, and 4 are incorrect, this option cannot be correct.

4. **Example of a Connecting Link**:
- The duck-billed platypus is a classic example of a connecting link. It has characteristics of both reptiles (e.g., it lays eggs) and mammals (e.g., it has mammary glands to feed its young). This duality exemplifies how a single organism can bridge two distinct groups.

5. **Conclusion**:
- Based on the analysis, the most accurate option is **Option 2: Link between two groups**. This option correctly captures the essence of what a connecting link represents in evolutionary biology.

### Final Answer:
**Option 2: Link between two groups**