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

Fact 2: Hemoglobin transports oxygen in blood.

Given the two facts above, answer the question "What is just one substance transported by hemoglobin?" with the following options: 
- gas
 - glucose
 - proteins
 - carbon
 - oxygen
 - an anion
 - hair
 - Energy


 

     oxygen    