在表中使用Regex c#查找href

I have html like this :

我有这样的html:

<table class="down_url_table_td_table">
    <tbody><tr>
        <td align="center">
                <a href="/go.html?url=https://dl121.dix3.com/downfile/nash20160419003/a5dd2131/a7b40b3e?md5=6825a9a1c6c564362e9de51a6efb2249" onclick="setCookie('vid1', 'e4d524c17d912066', 1*60*60*1000);">
            Click here to download</a> 
        </td>
    </tr>
    </tbody></table>
<table c