!!!!!!Как нажать радио кнопку на JS ??

Подскажите пожалуйста , как нажать 3-ю радиокнопку с помощью JS(сделать активной)?

<td><table width="100%" border="0" cellspacing="0" cellpadding="0">

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<td width="24"><img src="/order_images/freehostia/arrow.jpg"></td>

<td class="text" width="534"><strong>Add a Domain Name to Host:</strong></td>

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<td colspan="2" height="7"><img src="/order_images/freehostia/1px.gif" width="558" height="1"></td>

</tr>

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<td colspan="2" height="7"><table width="100%" border="0" cellspacing="1" cellpadding="0">

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<td bgcolor="#f6f6f6"><table border="0" cellspacing="0" cellpadding="0" onmouseover="this.style.cursor='pointer'" align="center">

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<td height="19" width="19" align="center"><div>

<input name="domain_type" id="domain_type_register_transfer" type="radio" value="register_transfer" onClick="showDomainField(this.value)" checked>

</div></td>

<td width="156" id="domain_holder_register_transfer" class="boldMe" onClick="triggerClick('domain_type_register_transfer')">Register new / Transfer</td>

<td height="19" width="19" align="center"><div>

<input name="domain_type" id="domain_type_existing" type="radio" value="existing" onClick="showDomainField(this.value)">

</div></td>

<td id="domain_holder_existing" class="unboldMe" onClick="triggerClick('domain_type_existing')" width="166">Use my existing domain</td>

<td height="19" width="19" align="center"><div>

<input name="domain_type" id="domain_type_subdomain" type="radio" value="subdomain" onClick="showDomainField(this.value)">

</div></td>

<td id="domain_holder_subdomain" class="unboldMe" onClick="triggerClick('domain_type_subdomain')" width="146">Use a subdomain</td>

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</table></td>