Air sacs of birds are helpful

Options

A. to lessen body weight
B. to keep body warm
C. to regulate body temperature
D. in blood circulation

Answer

**Step-by-Step Solution:**

1. **Understanding Air Sacs**: Air sacs are specialized structures found in the respiratory system of birds. They are part of the avian respiratory system and are located in various body cavities.

2. **Function of Air Sacs**: The primary function of air sacs is to facilitate continuous respiration. They allow for a more efficient exchange of gases (oxygen and carbon dioxide) during both inhalation and exhalation.

3. **Weight Reduction**: Air sacs also play a crucial role in reducing the overall weight of birds. By replacing some of the bone marrow in bones, air sacs make the skeletal structure lighter, which is essential for flight.

4. **Conclusion**: Therefore, the air sacs of birds are helpful primarily in lessening the body weight, which aids in flight.

5. **Final Answer**: The correct answer is option number 1: lessen the body weight.

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