Please read the following table in HTML format from a webpage and then answer the question in detail according to the table. Each table cell is defined by a <td> and a </td> tag. Each table row starts with a <tr> and ends with a </tr> tag. 'rowspan=m' and 'colspan=n' represents a cell spaning over 'm' rows and 'n' columns.

Webpage title:
Articulated buses in London
Table title:
Background
Table:
<table id='hittask' contenteditable='False'>
<tr> <th colspan=1 rowspan=1 > Route </th><th colspan=1 rowspan=1 > Commenced </th><th colspan=1 rowspan=1 > Ceased </th><th colspan=1 rowspan=1 > Operator </th><th colspan=1 rowspan=1 > Replaced by </th></tr>
<tr> <td colspan=1 rowspan=1 > 12 </td><td colspan=1 rowspan=1 > 6 November 2004 </td><td colspan=1 rowspan=1 > 4 November 2011 </td><td colspan=1 rowspan=1 > London Central </td><td colspan=1 rowspan=1 > double decker buses </td></tr>
<tr> <td colspan=1 rowspan=1 > 18 </td><td colspan=1 rowspan=1 > 15 November 2003 </td><td colspan=1 rowspan=1 > 12 November 2010 </td><td colspan=1 rowspan=1 > First London </td><td colspan=1 rowspan=1 > double decker buses </td></tr>
<tr> <td colspan=1 rowspan=1 > 25 </td><td colspan=1 rowspan=1 > 26 June 2004 </td><td colspan=1 rowspan=1 > 24 June 2011 </td><td colspan=1 rowspan=1 > East London </td><td colspan=1 rowspan=1 > double decker buses </td></tr>
<tr> <td colspan=1 rowspan=1 > 29 </td><td colspan=1 rowspan=1 > 14 January 2006 </td><td colspan=1 rowspan=1 > 25 November 2011 </td><td colspan=1 rowspan=1 > Arriva London </td><td colspan=1 rowspan=1 > double decker buses </td></tr>
<tr> <td colspan=1 rowspan=1 > 38 </td><td colspan=1 rowspan=1 > 29 October 2005 </td><td colspan=1 rowspan=1 > 13 November 2009 </td><td colspan=1 rowspan=1 > Arriva London </td><td colspan=1 rowspan=1 > double decker buses </td></tr>
<tr> <td colspan=1 rowspan=1 > 73 </td><td colspan=1 rowspan=1 > 4 September 2004 </td><td colspan=1 rowspan=1 > 2 September 2011 </td><td colspan=1 rowspan=1 > Arriva London </td><td colspan=1 rowspan=1 > double decker buses </td></tr>
<tr> <td colspan=1 rowspan=1 > 149 </td><td colspan=1 rowspan=1 > 24 April 2004 </td><td colspan=1 rowspan=1 > 15 October 2010 </td><td colspan=1 rowspan=1 > Arriva London </td><td colspan=1 rowspan=1 > double decker buses </td></tr>
<tr> <td colspan=1 rowspan=1 > 207 </td><td colspan=1 rowspan=1 > 9 April 2005 </td><td colspan=1 rowspan=1 > 9 December 2011 </td><td colspan=1 rowspan=1 > First London </td><td colspan=1 rowspan=1 > double decker buses </td></tr>
<tr> <td colspan=1 rowspan=1 > 436 </td><td colspan=1 rowspan=1 > 8 February 2003 </td><td colspan=1 rowspan=1 > 18 November 2011 </td><td colspan=1 rowspan=1 > London Central </td><td colspan=1 rowspan=1 > double decker buses </td></tr>
<tr> <td colspan=1 rowspan=1 > 453 </td><td colspan=1 rowspan=1 > 15 March 2003 </td><td colspan=1 rowspan=1 > 23 September 2011 </td><td colspan=1 rowspan=1 > Selkent London General (1) </td><td colspan=1 rowspan=1 > double decker buses </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > 507 </td><td colspan=1 rowspan=1 > 5 June 2002 </td><td class="highlighted"  colspan=1 rowspan=1 > 24 July 2009 </td><td colspan=1 rowspan=1 > London General </td><td class="highlighted"  colspan=1 rowspan=1 > single decker buses </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > 521 </td><td colspan=1 rowspan=1 > 5 June 2002 </td><td class="highlighted"  colspan=1 rowspan=1 > 31 August 2009 </td><td colspan=1 rowspan=1 > London General </td><td class="highlighted"  colspan=1 rowspan=1 > single decker buses </td></tr>
</table>
Question:
Which articulated vehicles in London were the first to be replaced?
Answer:
The first articulated vehicles to be replaced were 507 and 521, which were replaced by single-deck buses in 2009.