日期选择和显示的下拉菜单JS代码问题

请教各位达人，现在有如下的JS代码和其在HTML中调用，该代码为日期选择的下拉菜单，运行后自动显示当前系统日期，请问如何修改能使它打开后不要显示当前日期但仍能进行选择啊，并能正确列出每个月的天数呢？菜鸟一只，万分感谢～
<script type="text/javascript">
function createSelect(ActionFlag) {
var selYear = document.getElementById("tYEAR");
var selMonth = document.getElementById("tMON");
var selDay = document.getElementById("tDAY");
var dt = new Date();

if(ActionFlag == 1) {
MaxYear = dt.getFullYear();
MinYear = dt.getFullYear()-40;

for(var i = MaxYear; i >= MinYear; i--) {
var op = document.createElement("OPTION");
op.value = i;
op.innerHTML = i;
selYear.appendChild(op);
}
selYear.selectedIndex = 0;

for(var i = 1; i < 13; i++) {
var op = document.createElement("OPTION");
op.value = i;
op.innerHTML = i;
selMonth.appendChild(op);
}
selMonth.selectedIndex = dt.getMonth();
}

var date = new Date(selYear.value, selMonth.value, 0);
var daysInMonth = date.getDate();
selDay.options.length = 0;

for(var i = 1; i <= daysInMonth ; i++) {
var op = document.createElement("OPTION");
op.value = i;
op.innerHTML = i;
selDay.appendChild(op);
}
//alert();
selDay.selectedIndex = dt.getDate() - 1;
}
</script>


<td>
<select id="tYEAR" size="1" onChange="createSelect()"></select>
<select id="tMON" size="1" onChange="createSelect();"></select>
<select id="tDAY" size="1" ></select>
<script type="text/javascript">createSelect(1);</script> </td>

</tr>