DOM

HTML

<ul id="ul"></ul>
<select id="select">
    <option>1</option>
    <option>2</option>
    <option>3</option>
    <option>4</option>
    <option>5</option>
</select>
<br />
<button id="addLi">add li</button>
<button id="deleteOption">delete option</button>
<button id="addOption">add option</button>

JavaScript

var ul = $('#ul'), select = $('select'), addLi = $('#addLi'), deleteOption = $('#deleteOption'), addOption = $('#addOption'), count = 100;
//UL 中添加
addLi.bind('click', function(){
    ul.append('<li>new li</li>');
});

//Select 中删除
deleteOption.bind('click', function(){
    select.find('option:first').remove();
});

//Select 中添加
addOption.bind('click', function(){
    select.append('<option>'+ count +'</option>');
    count++;
});