Which situation(s)might warrant the removal of a histidine tag when purifying a recombinant protein?

A)Histidine residues inhibit protein folding,thereby decreasing the functionality of the protein.
B)Histidine residues bind preferentially to nickel resins on the column during purification,and are not washed away.
C)The expression vector used for inserting the gene of interest already contains histidine-encoding sequences.
D)All of the choices are correct.