According to the model of the human respiratory system, how do structures in the respiratory system interact to protect the lungs? How might a sinus infection affect the
rest of the respiratory system?

The circulatory and respiratory systems work together to circulate blood and oxygen throughout the body. Air moves in and out of the lungs through the trachea, bronchi, and bronchioles. Blood moves in and out of the lungs through the pulmonary arteries and veins that connect to the heart.

Explanation:

it has one origin of replication, but it proceeds in two directions - d)

i might be wrong but i think its a. let me know if i’m right and have a good rest of your day!