title: Why didn't show element inside the <div> if a value is selected in drop down box?
body: <p>I just wonder why the element inside the  didn't show up if a value is selected in drop drown box?But it is work fine in JSFiddle :<a href="http://jsfiddle.net/ca4Es/" rel="nofollow noreferrer">JSFiddle</a></p>
  
  <p>Below show how my HTML code and Jquery script work in my own system:</p>
  
  <pre><code>&lt;tr&gt;
                  &lt;th class="title"&gt;Registration&lt;/th&gt;
                  &lt;td&gt; : &lt;/td&gt;
                  &lt;th&gt;&lt;select name="reg" id="registration"&gt;
                          &lt;option value="No"&gt;No&lt;/option&gt;
                          &lt;option value="Yes"&gt;Yes&lt;/option&gt;
                      &lt;/select&gt;
                  &lt;/th&gt;
              &lt;/tr&gt;
              &lt;div id="opt" style="display:none;"&gt;
              &lt;tr&gt;
                  &lt;th class="title"&gt;Participant&lt;/th&gt;
                  &lt;td&gt; : &lt;/td&gt;
                  &lt;th&gt;&lt;input type="text" name="participant"&gt;&lt;/th&gt;
              &lt;/tr&gt;
  
              &lt;tr&gt;
                  &lt;th class="title"&gt;Payment Amount&lt;/th&gt;
                  &lt;td&gt; : &lt;/td&gt;
                  &lt;td&gt;&lt;input type="text" name="amount"&gt;&lt;/td&gt;
              &lt;/tr&gt;
  
              &lt;tr&gt;
                  &lt;th class="title"&gt;Payment Method&lt;/th&gt;
                  &lt;td&gt; : &lt;/td&gt;
                  &lt;td&gt;&lt;input type="radio" name="pay_method" value="CC"&gt;Credit Card
                  &lt;input type="radio" name="pay_method" value="Counter"&gt;Counter
                  &lt;/td&gt;
              &lt;/tr&gt;
              &lt;/div&gt;&lt;!--end of the opt--&gt;
  </code></pre>
  
  <p>Jquery script:</p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
  $(document).ready(function(){
  
   $("#registration").change(function(){
   if($(this).val()=="Yes"){
              $("#opt").show();
         }else {
          $("#opt").hide();   
         }
  
   });      
  }); 
  
     &lt;/script&gt;
  </code></pre>
  
  <p>The sample output as below:
         <img src="https://i.stack.imgur.com/wxShu.png" alt="enter image description here"> </p>
  
  <p>Supposed when the value No is selected,it will not showing anything,</p>