If Protein a Has a PI of 3

Multiple Choice

If protein A has a pI of 3.1, protein B has a pI of 6.8, and protein C has a pI of 8.9, which protein would elute FIRST from a cation exchange column at pH 7?

A) protein A
B) protein B
C) protein C
D) All three proteins would elute at the same time from the column.
E) Not enough information about the proteins is given in the problem.