Which CSS3 code fragment will style only the external l…

Which CSS3 code fragment will style only the external links in an HTML document?

A.
a: visitied { font-weight: bold; }

B.
a [href$= “http://”] { font-weight : bold; }

C.
a {font-weight: bold; }

D.
a [href^= “http://”] { font-weight : bold; }