the figure shows a diagrammatic view of human respiratory system with labels A, B , C and D . Select the option which given correct identification and main function and / or characteristic
A. D- lower end of lungs - diaphragm pulls it down during inspiration
B. A - trachea - long tube supported by complete cartilaginous rings for conducting inspired air
C. B - pleural membrane - surround ribs on both sides to provide cushion against rubbing
D. C - Alveoli , thin walled vascular bag like structures for exchange of gases