Which of the Following Interactions Causes a Change from the R

Multiple Choice

Which of the following interactions causes a change from the R state (oxy form) to the T state (deoxy form) of hemoglobin?

A) interactions between heme groups
B) protonation of the R-group of His146 on the $\beta$ subunit to allow formation of a salt bridge with Lys40 on the $\alpha$ subunit
C) salt bridge formed by $\alpha$ 1-Arg141 to the carboxylate of $\alpha$ 2Asp126
D) protonation of the $\alpha$ 1 subunit terminal carboxyl group disrupts a salt bridge with $\alpha$ 2Lys 127
E) none of the above