In birds, which one of the following is absent?

Options

A. Gall bladder
B. Urinary bladder
C. Teeth
D. All of these

Answer

To solve the question "In birds, which one of the following is absent?", we will analyze the options provided and identify which structures are typically absent in birds.

### Step-by-Step Solution:

1. **Understanding Bird Adaptations**:
- Birds are adapted for flight, which has led to the evolution of certain anatomical features that reduce weight. This adaptation often involves the loss or degeneration of specific organs.

2. **Analyzing the Options**:
- **Gallbladder**:
- The gallbladder is responsible for storing bile. In birds, this organ is absent as they have adapted to a diet that does not require bile storage.
- **Urinary Bladder**:
- The urinary bladder is used for the storage of urine. In birds, this organ is also absent. Instead, birds excrete waste through a structure called the cloaca, which serves multiple functions including excretion.
- **Teeth**:
- Birds do not have teeth. Instead, their jaws have evolved into beaks, which are more efficient for their feeding habits.

3. **Conclusion**:
- Since all three options (gallbladder, urinary bladder, and teeth) are absent in birds, the correct answer to the question is that all of these structures are absent.

### Final Answer:
- The correct answer is **option number 4: All of these**.

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