Assertion: Dinosaurs were connecting links between reptiles and birds.
Reason: They had characters of two different groups.

Options

A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion
B. If both Assertion and Reason are true and the Reason is not the correct explanation of the Assertion.
C. If Assertion is true but the Reason is false.
D. If both Assertion and Reason are false.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Dinosaurs were connecting links between reptiles and birds." To evaluate this, we need to understand what a connecting link is. Connecting links are organisms that exhibit characteristics of two different taxonomic groups.

2. **Analyzing the Reason**: The reason provided is that "They had characters of two different groups." This implies that dinosaurs should possess both reptilian and avian characteristics to be considered a connecting link.

3. **Evaluating the Characteristics of Dinosaurs**: Dinosaurs are classified as reptiles. They had features typical of reptiles, such as scales, and did not possess the avian characteristics needed to be considered a connecting link to birds.

4. **Identifying the True Connecting Link**: The true connecting link between reptiles and birds is Archaeopteryx, which exhibits both reptilian features (like teeth and a long tail) and avian features (like wings and feathers). Dinosaurs do not share these avian characteristics.

5. **Conclusion**: Since dinosaurs do not possess characteristics of both groups (reptiles and birds), the assertion is false. Additionally, the reason is also false because it incorrectly states that dinosaurs had characters of two different groups.

6. **Final Answer**: Therefore, both the assertion and the reason are false, which corresponds to option D.