\usepackage{color}
\usepackage[
%round, %(default) for round parentheses;
square, % for square brackets;
%curly, % for curly braces;
%angle, % for angle brackets;
%colon, % (default) to separate multiple citations with colons;
comma, % to use commas as separaters;
%authoryear,% (default) for author-year citations;
numbers, % for numerical citations;
%super, % for superscripted numerical citations, as in Nature;
sort, % orders multiple citations into the sequence in which they appear in