This Snippet explains how to enable Script Combining. For more details on why to use Script Combining, read Understanding Script Combining.
Note: for this to work, you must change the Version number in the Assembly attribute to match the version you're using.
<asp:ScriptManager ID="sm" runat="server">
<CompositeScript>
<Scripts>
<asp:ScriptReference Name="MicrosoftAjax.js" />
…