老师，我写的我的imooc下拉框老是有问题

html 

<div class="select_imooc" id="select_imooc">

<span>我的imooc ▼</span>

<!-- imooc下拉 -->

<ul class="select_imooc_item" id="select_imooc_item">

<li class="select_items">未完成订单</li>

<li class="select_items">已完成订单（退/改）</li>

<li class="select_items">我的保险</li>

<li class="select_items">查看个人信息</li>

<li class="select_items">账户安全</li>

<li class="select_items">常用联系人</li>

<li class="select_items">重点旅客预约</li>

<li class="select_items">遗失物品查找</li>

<li class="select_items">服务查询</li>

<li class="select_items">投诉</li>

<li class="select_items">建议</li>

</ul>

</div>

css

/*下拉框*/

.select_imooc{

float: right;

position: relative;

color: black;

padding:0 30px 0 5px;

}

/*下拉框ul*/

.select_imooc_item{

display: none;

position: absolute;

padding:15px 0 15px 0;

    top: 100px;

    left: 0;

    list-style: none;

    line-height: 25px;

    font-size: 12px;

    background: white;

    color: gray;

    border: 1px solid #fb7403;

}

/*下拉框li*/

.select_items{

padding: 2px 10px;

}

.select_items:hover{

color: black;

}

.select_items:nth-child(3n){

border-top: 1px dashed gray;

border-bottom: 1px dashed gray;

}

js

//下拉框挂移入事件

addHandler(select_imooc,'mouseover',function(){

event.stopPropagation();

this.style.color = '#03fb16';

selectUl.style.display = 'block';

})

addHandler(select_imooc,'mouseout',function(){

// event.stopPropagation();

this.style.color = '#000';

selectUl.style.display = 'none';

})

没有报错 但是我每次移入显示出的下拉框列表时 总是在移到服务查询这一项时 下拉列表就消失了 我还没有移出下拉列表 服务查询这一项的下面还有两项 我看了好几遍也不知道问题出在哪里