Which of the Following Is True Regarding the Effectors of Hemoglobin-Oxygen

Which of the following is true regarding the effectors of hemoglobin-oxygen binding?

A) an increase in blood pH will cause hemoglobin to bind more tightly to oxygen
B) increased CO₂ from increased muscle activity will result in an increase in the R state of hemoglobin
C) increased Cl^- will cause the formation of a salt bridge between two Lys residues, one on an $\alpha$ subunit, the other on a $\beta$ subunit
D) the binding site of 2,3-BPG contains several Asp and Glu residues which are repelled by the similar charge, pushing the two $\beta$ subunits away from each other
E) all of the above