The first animals to fly were

Options

A. Mammals
B. Lizards
C. Birds
D. Insects.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the first animals to evolve the ability to fly. This requires knowledge of evolutionary history and the timeline of flight development in various animal groups.

2. **Identifying the Options**: The options provided are mammals, lizards, birds, and insects. We need to analyze which of these groups was the first to develop flight.

3. **Researching Evolutionary History**: Based on evolutionary studies, it is known that insects were the first animals to evolve flight. This is supported by fossil evidence.

4. **Examining Fossil Evidence**: The earliest fossil evidence of flying insects dates back to the Carboniferous period, approximately 410 million years ago. These early flying insects were similar to modern dragonflies.

5. **Conclusion**: Based on the evidence and analysis, the correct answer to the question "The first animals to fly were" is **insects**.

---