I needed more help on my assignment soo

1. Our bodies exhale carbon dioxide (CO 2 ). Carbon dioxide . (more than one answer)
A.) is a compound
B.) has two atoms of oxygen
C.) is made of oxygen and carbon
D.) is an element
E.) has two molecules of oxygen
2. Atomic mass is calculated by adding(protons, electrons, OR isotopes) and(molecules, protons, OR neutrons).
3. The chemical formula for magnesium oxide is 2MgO. The number 2 represents the number of ___.
A.) oxygen atoms
B.)magnesium atoms
C.)magnesium oxide molecules