The figure shows a diagrammatic view of human respiratory system with labels A, B,C and D. Select the option which gives correct identification and main function and/or characteristic.

A

D-Lower end of lungs -diaphragm pulls it down during inspiration

B

A-trachea-lung-long tube supported by complete cartilaginous rings for conducting inspired air.

C

B-pleural membrane -surround ribs on the both sides to provide cushion against rubbing.

D

C-Alveoli-walled vascular bag like structures for exchange of gases