Which of these is a CSS pseudo class?
A) .abc
{
color:green;
}

B) a:visited
{
color:green;
}

C) h1 h2
{
color:green;
}

a:visited
CSS pseudo classes are defined using this syntax
selector:pseudo-class {property:value;}
a->selector
visited-->pseudo-class
color-->property
green-->value

They are meant for special effects.(color of the clicked hyperlink in this case).