During quiet breathing, inhalation is ... whereas exhalation is ...

Options

A. passive, passive
B. passive, active
C. active, active
D. active, passive

Explanation

### Step-by-Step Solution:

1. **Understanding Quiet Breathing**:
- Quiet breathing, also known as tidal breathing, refers to the normal, relaxed breathing that occurs without any forceful inhalation or exhalation.

2. **Identifying the Phases of Breathing**:
- Breathing consists of two main phases:
- **Inhalation (Inspiration)**: The process of taking air into the lungs.
- **Exhalation (Expiration)**: The process of expelling air from the lungs.

3. **Role of the Diaphragm**:
- The diaphragm is a dome-shaped muscle located beneath the lungs. Its contraction and relaxation are crucial for the breathing process.
- When the diaphragm contracts, it increases the volume of the thoracic cavity, leading to a decrease in pressure within the lungs, allowing air to flow in (inhalation).
- Conversely, when the diaphragm relaxes, the volume of the thoracic cavity decreases, increasing pressure in the lungs, which forces air out (exhalation).

4. **Determining the Nature of Inhalation and Exhalation**:
- Inhalation requires the active contraction of the diaphragm, making it an **active process**.
- Exhalation occurs due to the passive relaxation of the diaphragm, making it a **passive process**.

5. **Final Answer**:
- Therefore, during quiet breathing, inhalation is **active**, whereas exhalation is **passive**.