Which one is the distinguishing feature of all vertebrates :

Options

A. An internal bony or cartilagenous skeleton
B. A hairy body covering
C. Presence of mammary glands
D. Open type of Circulatory system

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the distinguishing feature of all vertebrates. This means we need to identify a characteristic that is common to all members of the vertebrate group.

2. **Evaluating the Options**:
- **Option 1: Internal body or cartilaginous skeleton**: This option suggests that vertebrates have an internal skeleton made of cartilage or bone. This is indeed a defining characteristic of vertebrates, as they all possess a backbone or vertebral column.
- **Option 2: Hairy corneal covering**: This option refers to a feature that is not applicable to all vertebrates. It is more specific to mammals, which have hair or fur.
- **Option 3: Presence of mammary glands**: This feature is specific to mammals and is not found in all vertebrates. Therefore, it cannot be the distinguishing feature of all vertebrates.
- **Option 4: Open type circulatory system**: This option describes a circulatory system found in invertebrates, such as arthropods, and is not a characteristic of vertebrates, which have a closed circulatory system.

3. **Identifying the Correct Answer**: Based on the evaluation of the options, the correct answer is **Option 1: Internal body or cartilaginous skeleton**. This feature is indeed the distinguishing characteristic of all vertebrates.

### Final Answer:
The distinguishing feature of all vertebrates is the **internal body or cartilaginous skeleton**.

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