Read the following text and answer the following questions on the basis of the same:
Transgenic animals have their DNA manipulated to possess and express an extra gene. The genome of these animals has been changed and they can carry genes from other species. The first transgenic sheep was Tracy. The reason behind producing these transgenic animals are for specific economic trait, some are produced as disease models (animals genetically manipulated to exhibit disease symptoms so that effective treatment can be studied)
___ were the first mammals to be transgenic animals.

Options

A. Sheep
B. Mice
C. Fruit flies
D. None of these

Explanation

To answer the question, "___ were the first mammals to be transgenic animals," we need to analyze the information provided in the text.

### Step-by-Step Solution:

1. **Identify the Key Information**: The text states that transgenic animals have their DNA manipulated to possess and express an extra gene. It mentions that the first transgenic sheep was named Tracy.

2. **Determine the First Transgenic Animal**: The transcript mentions that the first transgenic animal was created in 1974 by Rudolf Zeynisch, and it specifically states that this first transgenic animal was a mouse.

3. **Conclusion**: Based on the information provided, the first mammals to be transgenic animals were mice.

### Final Answer:
Mice were the first mammals to be transgenic animals.

---