How to add class?

How to add class?

Hello,

I am new in JQuery.

How can i add class to "UK" using JQuery method?

I am reach at
$('.folder-open-last > span').addClass("active1");

<ul>
    <li id="17" class="folder-open-last">
        <img border="0" src="js/jquery/plugins/simpleTree/images/spacer.gif" class="trigger" style="float: left;">
        <span class="text">Europe</span>
       
        <ul style="display: block;">
            <li class="line">&nbsp;</li>
            <li id="19" class="folder-open">
                <img border="0" src="js/jquery/plugins/simpleTree/images/spacer.gif" class="trigger" style="float: left;">
                <span class="text">UK</span>
               
                <ul style="display: block;">
                    <li class="line-last"></li>
                </ul>
            </li>
            <li class="line">&nbsp;</li>
            <li id="31" class="folder-open-last">
                <img border="0" src="js/jquery/plugins/simpleTree/images/spacer.gif" class="trigger" style="float: left;">
                <span class="text">test</span>
               
                <ul style="display: block;">
                    <li class="line-last"></li>
                </ul>
            </li>
            <li class="line-last"></li>
        </ul>
    </li>
</ul>

Please guide me.

Thanks in advance.