Which of these will be seen in our respiratory system ?
I. The absence of cartilage in small bronchioles allows them to expand .
II. The walls of the alveoli are made of cuboidal epithelium .
III. The recoil of the elastic fibres surrounding the alveoli helps to move air out during expiration.
IV. The trachea and bronchi are supported by circles of cartilage.

Options

A. I and II
B. I and III
C. II and IV
D. III and IV

Answer

To solve the question regarding which statements are true about the respiratory system, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I: The absence of cartilage in small bronchioles allows them to expand.**
- **Analysis:** This statement is true. Small bronchioles do not have cartilage in their walls, which allows them to be more flexible and expand during breathing.

2. **Statement II: The walls of the alveoli are made of cuboidal epithelium.**
- **Analysis:** This statement is false. The walls of the alveoli are made of simple squamous epithelium, which is thin and allows for efficient gas exchange. Therefore, this statement does not accurately describe the respiratory system.

3. **Statement III: The recoil of the elastic fibers surrounding the alveoli helps to move air out during expiration.**
- **Analysis:** This statement is true. The elastic fibers in the alveolar walls do indeed help in the process of expiration by recoiling and pushing air out of the lungs.

4. **Statement IV: The trachea and bronchi are supported by circles of cartilage.**
- **Analysis:** This statement is partially true but misleading. The trachea and bronchi are supported by C-shaped rings of cartilage (not complete circles), which provide structural support and keep the airways open.

### Conclusion:
Based on the analysis:
- Statements I and III are true.
- Statement II is false.
- Statement IV is misleading as it refers to "circles" instead of "C-shaped rings."

Thus, the correct statements that can be seen in our respiratory system are **I and III**.

### Final Answer:
The correct options are I and III.

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