Oxygen and carbon dioxide travels to and from tiny air sacs in the lungs, through the walls of the capillaries, into the blood. Blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs.

Answer:
Increasing the number of trusses increases the strength of the bridge.
Explanation:
Just had this question
b is the right answer because we breathe oxygen and when we breathe out we let out carbon dioxide