select box에는 onclick이 안되나요??

<div id="change-font-box" class="change-font-box">

  <input type="radio" name="ct_fontsize1" class="change-font-btn" onclick="changeFontSize('')">
      보통
  </input>
  &nbsp;
  <input type="radio" name="ct_fontsize2" class="change-font-btn" onclick="changeFontSize('-')" >
      작은글씨
  </input>
  &nbsp
  <input type="radio" name="ct_fontsize3" class="change-font-btn" onclick="changeFontSize('+')">
      큰 글씨
  </input>

</div>

 

<div id="change-font-box" class="change-font-box">
  <select class="change-font-btn" onclick="changeFontSize('')">
  <input type="radio" name="ct_fontsize1" value="">
      보통
  </input>
  &nbsp;
  <input type="radio" name="ct_fontsize2" value="-">
      작은글씨
  </input>
  &nbsp
  <input type="radio" name="ct_fontsize3" value="+">
      큰 글씨
  </input>
</select>
</div>

 

<script type="text/javascript">
            function changeFontSize(type) {
                var fontSize = $('html').css('font-size');
                fontSize = Number(fontSize.substr(0,fontSize.length-2));
                if(type === '+') {
                    fontSize += 5;
                } else if(type === '-') {
                    fontSize -= 5;
                } else {
                    fontSize = 16;
                }
                var percent = (fontSize/16)*100;
                $('textarea, input').css('font-size',percent+'%');
                $('.change-font-btn').blur();
            }
            </script>