Gas exchange in lungs/ gas transport in blood

1. How is hemoglobin's affinity for oxygen affected by the presence or absence of oxygen?
Rank hemoglobin molecules with the described conditions from most likely to bind oxygen molecules to most likely to release oxygen molecules.
1 bound O2, Po2=100mmHg
3 bound O2, Po2=40mmHg
1 bound O2, Po2=40mmHg
3 bound O2, Po2=100mmHg

2. True or false? The lungs of humans form from the embryonic foregut.
   
3. How is most carbon dioxide transported from tissues to the lungs?
   
   As bicarbonate ions ({\rm HCO_3}{^{-}}).
   As carbon dioxide gas.
   As carbonic acid.
   As protons (\rm H^+).
 
4. Which of the following statements about the oxygen-hemoglobin interaction is true?
   
   Each hemoglobin molecule can bind one oxygen molecule.
   The binding of one oxygen molecule to hemoglobin stimulates the unloading of the oxygen molecules that are already bound.
   The oxygen–hemoglobin dissociation curve is exponential, which means that hemoglobin can respond quickly to small changes in oxygen demand.
   The binding of one oxygen molecule to hemoglobin stimulates the binding of other oxygen molecules.

Also, please view the attached file!!! I have a question on that too!