C# 如何用正则表达式提取下面的内容

Question

<tr class=thead><td>109.74.51.211</td><td><img border=0 src=/picit.php?q=BQN%253Q></td><td>High Anonymous</td><td>-</td><td>-</td><td>-</td><td>00:02:32</td></tr>
<tr ><td>190.204.178.189</td><td><img border=0 src=/picit.php?q=BQN4ZN%253Q%253Q></td><td>High Anonymous</td><td>-</td><td>-</td><td>-</td><td>00:03:34</td></tr>
<tr class=thead><td>190.206.106.82</td><td><img border=0 src=/picit.php?q=BQN4ZN%253Q%253Q></td><td>High Anonymous</td><td>-</td><td>-</td><td>-</td><td>00:03:34</td></tr>
<tr ><td>41.217.164.78</td><td><img border=0 src=/picit.php?q=BQN4ZN%253Q%253Q></td><td>High Anonymous</td><td>-</td><td>-</td><td>-</td><td>00:04:35</td></tr>
<tr class=thead><td>91.99.224.106</td><td><img border=0 src=/picit.php?q=BQN%253Q></td><td>High Anonymous</td><td><img border=0 src=/images/country_icons/ir.gif>&nbsp;IRAN, ISLAMIC REPUBLIC OF</td><td>-</td><td>-</td><td>00:04:35</td></tr>
<tr ><td>186.207.138.4</td><td><img border=0 src=/picit.php?q=BQN4ZN%253Q%253Q></td><td>High Anonymous</td><td>-</td><td>-</td><td>-</td><td>00:05:38</td></tr>
<tr class=thead><td>212.45.12.10</td><td><img border=0 src=/picit.php?q=ZmRlBN%253Q%253Q></td><td>High Anonymous</td><td><img border=0 src=/images/country_icons/ru.gif>&nbsp;RUSSIAN FEDERATION</td><td>MOSKVA</td><td>MOSCOW</td><td>00:05:38</td></tr>
如何写正则表达式提取上面内容中蓝色的字段， 就是提取所有包含红色字段的行里的蓝色字段。
本人菜鸟，试了很久还是得不到结果，望高手来。

Answer 1

            string str = @"<tr class=thead><td>109.74.51.211</td><td><img border=0 src=/picit.php?q=BQN%253Q></td><td>High Anonymous</td><td>-</td><td>-</td><td>-</td><td>00:02:32</td></tr>
<tr ><td>190.204.178.189</td><td><img border=0 src=/picit.php?q=BQN4ZN%253Q%253Q></td><td>High Anonymous</td><td>-</td><td>-</td><td>-</td><td>00:03:34</td></tr>
<tr class=thead><td>190.206.106.82</td><td><img border=0 src=/picit.php?q=BQN4ZN%253Q%253Q></td><td>High Anonymous</td><td>-</td><td>-</td><td>-</td><td>00:03:34</td></tr>
<tr ><td>41.217.164.78</td><td><img border=0 src=/picit.php?q=BQN4ZN%253Q%253Q></td><td>High Anonymous</td><td>-</td><td>-</td><td>-</td><td>00:04:35</td></tr>
<tr class=thead><td>91.99.224.106</td><td><img border=0 src=/picit.php?q=BQN%253Q></td><td>High Anonymous</td><td><img border=0 src=/images/country_icons/ir.gif>&nbsp;IRAN, ISLAMIC REPUBLIC OF</td><td>-</td><td>-</td><td>00:04:35</td></tr>
<tr ><td>186.207.138.4</td><td><img border=0 src=/picit.php?q=BQN4ZN%253Q%253Q></td><td>High Anonymous</td><td>-</td><td>-</td><td>-</td><td>00:05:38</td></tr>
<tr class=thead><td>212.45.12.10</td><td><img border=0 src=/picit.php?q=ZmRlBN%253Q%253Q></td><td>High Anonymous</td><td><img border=0 src=/images/country_icons/ru.gif>&nbsp;RUSSIAN FEDERATION</td><td>MOSKVA</td><td>MOSCOW</td><td>00:05:38</td></tr>";
            Regex reg = new Regex(@"(?is)<tr[^>]*?><td>([^>]+)</td><td><img[^>]*?src=(['""\s]?)[^=]+=BQN4ZN%253Q%253Q\2[^>]*?></td>.*?</tr>");
            foreach (Match m in reg.Matches(str))
                Console.WriteLine(m.Groups[1].Value);
/*
190.204.178.189
190.206.106.82
41.217.164.78
186.207.138.4*/

Answer 2

            System.IO.StreamReader reader = new System.IO.StreamReader("e:\\1.txt");
            string s = reader.ReadToEnd();
            System.Text.RegularExpressions.Regex reg = new System.Text.RegularExpressions.Regex(@"(?is)(?<=<tr[^>]*?><td>)[^>]+(?=</td><td><img[^>]*?=BQN4ZN%253Q%253Q></td>.*?</tr>)");
            System.Text.RegularExpressions.MatchCollection ms = reg.Matches(s);
            foreach (System.Text.RegularExpressions.Match m in ms)
            {
                MessageBox.Show(m.Value);
            }