Material Design Bootstrap选择下拉箭头问题

Question

请查找错误附件

<select class="mdb-select">
   <option value="" disabled selected >Choose your option</option>
   <option value="1">Option 1</option>
   <option value="2">Option 2</option>
   <option value="3">Option 3</option>
</select>

JavaScript代码

$(document).ready(function() {
            $('.mdb-select').material_select();`enter code here`
         });