The respiratory system is derived from which germ layer?

In humans,the oblique fissure is present in

Which part of the thyroid cartilage is closed?

Friction on the lung surface is reduced by:

The alveolar sac of the lungs and the villi of the intestine have a similar function,which is that:

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