Jquery 比较年份验证不适用于多个选择框

我试着比较两年，即从一年到两年。我有多个选择框。对于每个选择框，我必须进行比较

//From year selectbox
<select id="exp_year<?php echo $n;?>" name="exp_year[<?php echo $n;?>]" class="input exp_year" tabindex="20">
     <option value="">Years</option>
        <?php $year = date('Y');
              for($i=1970;$i<=$year;$i++)
              { ?>
                  <option value="<?php echo $i; ?>" <?php echo $exp_year==$i ? "selected":""; ?>><?php echo $i; ?></option>
        <?php }  ?>
 //To year select box
 <select id="toexp_year<?php echo $n;?>" name="toexp_year[<?php echo $n;?>]" class="input toexp_year" tabindex="22">
   <option value="">Years</option>
    <?php $year = date('Y');
    for($i=1970;$i<=$year;$i++)
    { ?>
        <option value="<?php echo $i; ?>" <?php echo $toexp_year==$i ? "selected":""; ?>><?php echo $i; ?></option>
<?php }  ?>
 </select>

 //jquery code to add select box:
 $("#tbody").append('<tr><td align="center">'+ln+'</td><td><input type="text" name="company_name['+ln+']" value="" id="company_name'+ln+'" class="input" style="width:160px !important;"/></td><td><input type="text" name="designation['+ln+']" id="designation'+ln+'" value="" class="input" style="width:160px !important;"></td><td><select name="exp_month['+ln+']" id="exp_month'+ln+'" class="input"><option value="">Months</option><option value="Jan">Jan</option><option value="Feb">Feb</option><option value="Mar">Mar</option><option value="Apr">Apr</option><option value="May">May</option><option value="Jun">Jun</option><option value="Jul">Jul</option><option value="Aug">Aug</option><option value="Sep">Sep</option><option value="Oct">Oct</option><option value="Nov">Nov</option><option value="Dec">Dec</option></select>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<select id="exp_year'+ln+'" name="exp_year['+ln+']" class="input exp_year"><option value="">Years</option><?php $year = date('Y');for($i=1970;$i<=$year;$i++){ ?><option value="<?php echo $i; ?>"><?php echo $i; ?></option><?php } ?></select>&nbsp;&nbsp;To&nbsp;&nbsp;<select id="toexp_month'+ln+'" name="toexp_month['+ln+']" class="input"><option value="">Months</option><option value="Jan">Jan</option><option value="Feb">Feb</option><option value="Mar">Mar</option><option value="Apr">Apr</option><option value="May">May</option><option value="Jun">Jun</option><option value="Jul">Jul</option><option value="Aug">Aug</option><option value="Sep">Sep</option><option value="Oct">Oct</option><option value="Nov">Nov</option><option value="Dec">Dec</option></select>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<select id="toexp_year'+ln+'" name="toexp_year['+ln+']" class="input toexp_year"><option value="">Years</option><?php $year = date('Y');for($i=1970;$i<=$year;$i++){ ?><option value="<?php echo $i; ?>"><?php echo $i; ?></option><?php }  ?></select></td></tr></br></br>');

我们如何编写代码呢？

示例HTML

<select name="month" id="start_d"class="required select">
        <option value="">From Month</option>
        <option>1970</option>
        <option>1971</option>
    </select>
    <select name="day" id="end_d" class="required select">
        <option value="">To Month</option>
        <option>1969</option>
        <option>1970</option>
    </select>

剧本

$(document).ready(function() {
    $("#end_d").on('change',function(){
        var f_m=$('#start_d').val()
        if($(this).val() < f_m)
        {
          alert('Choose "To Year" Greater Than "From Year"')            
        }
    });
});

---

您必须验证的条件是什么？到年必须大于从年。哪个选择框应该验证哪个？到年选择框从年验证选择框..这里我有多个选择框。我必须验证每个选择框。验证意味着什么条件？当我添加另一个选择框时，此条件仅适用于第一个选择框。此条件不起作用。