Which of the following prevents the collapse of the trachea?

What are the membranes covering the lungs called?

Identify the component of the respiratory system which displays the features given below and choose the correct option:
$I.$ Double layered
$II.$ Fluid contained in it reduces the friction on the lung surface
$III.$ Its outer layer is in contact with the thoracic wall
$IV.$ Its inner layer is in contact with the lungs

Which part of the thyroid cartilage is closed?

What is the number of tracheal cartilaginous rings in humans?

$A$ pair of external nostrils present in humans opens out