Get all HTML SPAN tags having the particular class name using Regular Expressions in C#

Can any one give me a code to read the span having the particular class name and assign to match collection.

I am having a set of html tags.

<span><a href="asb.aspx">Dummy</a></span>

<span class="active"><a href="abc.aspx">Hi thi is titile</a></span>

I need to get the span having the class name ="active".That is i need the result

<span class="active"><a href="abc.aspx">Hi thi is titile</a></span>

.It will be fine if i get the text in the a tag that is with in the span having the class name

"active".

Thanks.