Give reason : The whale is a mammal.

Explanation

**Step-by-Step Solution:**

1. **Definition of Mammals**: First, we need to understand what defines a mammal. Mammals are a class of animals characterized by certain features such as the presence of mammary glands, hair or fur, and the ability to give live birth (with some exceptions).

2. **Presence of Mammary Glands**: One of the key features that classify an animal as a mammal is the presence of mammary glands. These glands allow female mammals to produce milk to nourish their young. Whales, including the blue whale, possess mammary glands, which is a strong indication of their classification as mammals.

3. **Respiration through Lungs**: Unlike fish that breathe through gills, whales breathe air using lungs. This is another characteristic feature of mammals. Whales must come to the surface of the water to breathe, which aligns with the respiratory system of mammals.

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