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<script language="JavaScript">function newlist(obj,n,t){  obj.options.length = t-n+1;  for(var ii=n; ii<=t; ii++)  {    obj.options[ii-n].text = ii    obj.options[ii-n].value = ii  }}function dateSelect(){  var y = year.value;  var m = month.value;  var d = new Date(y,m,0)  var k = d.getDate();  newlist(day,1,k);}</script><select size="1" name="year" onchange="dateSelect()"></select>年<select size="1" name="month" onchange="dateSelect()"></select>月<select size="1" name="day"></select>日<script language="JavaScript">newlist(year,2000,2020);newlist(month,1,12);dateSelect();</script>