Which one of the following is surrounded by a rich amount of capillaries?

The correct option is A Alveoli
$\bullet$ The alveoli are surrounded by tiny blood vessels, called capillaries. It is the alveoli that receive the oxygen and pass it on to the blood.
$\bullet$ Alveoli and capillaries both have very thin walls, which allow the oxygen to pass through simple diffusion.
$\bullet$ Trachea, also called the windpipe, is a cartilaginous tube that connects the pharynx and larynx to the lungs.
$\bullet$ Nostril is either of the two external openings of the nasal cavity that allows air to enter the lungs.
$\bullet$ Bronchi are the air passages into the lungs.