void Main()
{
 
string hcontent2=@"<table>
  <tr><td>aaaaa</td></tr>
  <tr><td>aabcb</td></tr>
  <tr><td>bbbb</td></tr>
</table>";
foreach(Match m in Regex.Matches(hcontent2, @"(?i)<tr>.*?abc.*?</tr>"))
    {
    Console.WriteLine(m.Value); 
    }
    /* 
    <tr><td>aabcb</td></tr
    */
}

------解决方案--------------------
目标为什么是:
 <tr>
Tar_Candle
</tr>

------解决方案--------------------

C# code

void Main()
{
    string hcontent2=@"<table>
<tr>
12343
<tr>
<tr>
3454afsadf35
<tr>
</table>
<table>
<tr>
<table>
<tr>
Tar_Candle
</tr>
</table>
</tr>
<tr>
Tar_Abc
</tr>
<tr>
aaa
</tr>
</table>
<table>
<tr>
adaf
</tr>
<tr>
xys
</tr>
</table>";
foreach(Match m in Regex.Matches(hcontent2, @"(?is)<tr>((?!</?tr>).)*?Candle((?!</tr>).)*?</?tr>"))
    {
    Console.WriteLine(m.Value); 
    }
    /* 
    <tr>
    Tar_Candle
    </tr>
    */

}