Pulmonary circulation transports blood through the alveoli for gas exchange. In this circulation the blood that comes from the veins initially has low oxygenation, and then leaves the right ventricle of the heart through the pulmonary artery, enters the lungs and returns to the heart with arterial and oxygenated blood
The bronchial circulation is well oxygenated and provides oxygen to the lungs. The structures to which this oxygen contributes in lungs are those that do not participate in a gas exchange.
Firstly, it cannot be bacteria because bacteria is prokaryotic with no membrane bound organelles. And it's cell wall is made of murein (peptidoglycan).
It certainly isn't a virus virus because a virus has no true cellular structure.
Let's see why we ruled out the other 3 eukaryotic kingdoms:
It can't be an animal because animal cells don't have cell walls and are multicellular.
It can't be fungi because its cell wall is made of chitin, not cellulose.
It can't be a plant because plants are all multicellular.
