If a molecule of co2 released into the blood in your left toe is exhaled from your nose, it must passed all the following excepta. the pulmonary veinb. the tracheac. right atriumd. right ventricle

The correct answer is option a, that is, pulmonary vein.

Explanation:

After getting discharged from the left toe, the molecule of carbon dioxide is exhaled through the nose, and in the process, it moves via the trachea, the alveoli, the right ventricle, and the right atrium. However, it does not passes through the pulmonary vein as the prime function of the pulmonary vein is to carry oxygenated blood obtained from the lungs and to pass it to the heart's left atrium.  

The pulmonary vein is different from other veins found within the body, which carries deoxygenated blood or blood filled with carbon dioxide from different parts of the body to the heart. Thus, it is clear that carbon dioxide does not pass through the pulmonary vein.  

what's the rest of the question

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.