Task: Question Answering
Input (English): Question: The binding of O2 to hemoglobin: 
 Options:  <1> Follow a hyperbolic kinetics. <2> It favors the transition from Fe2 + to Fe3 + in the heme group of the protein. <3> Induces the deprotonation of the protein. <4> It is facilitated in the presence of 2,3bisphosphoglycerate. <5> It is carried out through a covalent interaction with Fe3 +.
Output (English): 3