Generally the breathing system in birds :

Options

A. is identical to the human breathing system
B. is merely accelerated by the flight muscles
C. resembles the positive pressure system of a frog
D. requires a flow-through bronchi-lung so constant oxygen absorption can meet the high oxygen demand

Explanation

**Step-by-Step Solution:**

1. **Understanding the Breathing System in Birds**: Birds have a unique respiratory system that is different from mammals. Their breathing system is designed to meet the high oxygen demands required for flight.

2. **Identifying the Nature of Airflow**: The airflow in birds is unidirectional. This means that air flows in one direction through their respiratory system, allowing for more efficient gas exchange.

3. **Analyzing the Options**:
- **Option A**: "Identical to the human breathing system" - This is incorrect because birds do not have alveoli like humans; instead, they have air capillaries.
- **Option B**: "Merely accelerated by the flight muscles" - This is also incorrect as the flight muscles are not directly related to the breathing mechanism.
- **Option C**: "Resembles the positive pressure system of a frog" - This is incorrect because frogs utilize a different mechanism for breathing that involves positive pressure, which is not applicable to birds.
- **Option D**: "Requires a flow through bronchi lung so constant oxygen absorption can meet the high oxygen demand" - This is correct. Birds require a continuous flow of air through their lungs to maintain high oxygen absorption.

4. **Conclusion**: The correct answer is that the breathing system in birds requires a flow through bronchi lung so constant oxygen absorption can meet the high oxygen demand.

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