The "Selectivity Filter" in an Ion Channel Is Most Accurately

The "selectivity filter" in an ion channel is most accurately described as a part of the pore that

A) contains a ring of uncharged residues that interact with specific ions.
B) contains a ring of charged residues that interact with specific ions.
C) contains a ring of charged residues that change conformation to either open or close access through the pore for ions.
D) contains a ring of uncharged residues that change conformation to either open or close access through the pore for ions.
E) interacts with lipids.