The aquatic animal whose skeleton is made almost entirely of cartilage is

Options

A. dolphin
B. shark
C. whale
D. penguin.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for an aquatic animal whose skeleton is primarily made of cartilage. This means we need to identify an animal that does not have a bony skeleton.

2. **Identifying Types of Aquatic Animals**: We need to consider various types of aquatic animals such as mammals (like dolphins and whales), birds (like penguins), and fish (like sharks).

3. **Analyzing Mammals**: Dolphins and whales are both mammals. Mammals typically have a bony skeleton, so they do not fit the criteria of having a skeleton made almost entirely of cartilage.

4. **Considering Birds**: Penguins are birds and, like mammals, they also have a bony skeleton. Therefore, they cannot be the correct answer either.

5. **Focusing on Fish**: Sharks are a type of fish known as cartilaginous fish. They have skeletons made almost entirely of cartilage, which fits the criteria of the question.

6. **Conclusion**: Based on the analysis, the aquatic animal whose skeleton is made almost entirely of cartilage is the shark.

**Final Answer**: The aquatic animal whose skeleton is made almost entirely of cartilage is the shark.

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