<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>- jsFiddle demo by vlasenkofedor</title>
<script type='text/javascript' src='http://code.jquery.com/jquery-1.9.1.js'></script>
<style type='text/css'>
#block a {
color: red;
display: block;
}
#block a.act {
color: green;
}
</style>
</head>
<body>
<div id="block">
<a>Привет</a>
<a>дорогие</a>
<a>друзья</a>
</div>
<script>
(function ($) {
$('#block a').on('click', function () {
$(this).siblings().removeClass('act').end().addClass('act');
})
})(jQuery);
</script>
</body>