Fact 1: Oxygen is just one substance transported by the blood.

Fact 2: Blood is transported through our veins.

Given the two facts above, answer the question "Oxygen is just one substance transported through our what" with the following options: 
- hair
 - lungs
 - mucus
 - matter
 - ovaries
 - veins
 - bones
 - skin


 

      veins   