bootstrap的响应式导航条

当导航栏内存在表单的时候,使用响应式导航条会出现两个这样的滚动条,怎么避免这种情况的产生呢?

<div class="navbar navbar-inverse">

    <!--navbar-inverse和navabar-default,前者是黑色,后者是灰色-->

    <div class="navbar-header">

        <button class="navbar-toggle" data-target="#hamb2" data-toggle="collapse">

            <span class="icon-bar"></span>

            <span class="icon-bar"></span>

            <span class="icon-bar"></span>

        </button>

        <div class="navbar-brand">

            <span class="highlight">7thHeaven</span>

            </div>

    </div>

    <div id="hamb2" class="collapse navbar-collapse navbar-responsive-collapse">

       <ul class="nav navbar-nav">

           <li class="active"><a href="#">Home</a></li>

               <li><a href="#">首页</a></li>

                <li class="btn-group">

                <a href="" class="dropdown-toggle" data-toggle="dropdown">课程列表<span class="caret"></span></a>

            <ul class="dropdown-menu">

                <li class="dropdown-header">前端</li>

                <li><a href="#">HTML5</a></li>

                <li><a href="#">CSS3</a></li>

                <li><a href="#">Vue.js</a></li>

                <li><a href="#">JQuery</a></li>

                <li class="nav-divider"></li>

                <li class="dropdown-header">Java</li>

                <li><a href="#">Java</a></li>

                <li><a href="#">Java</a></li>

                <li><a href="#">Java</a></li>

                <li><a href="#">Java</a></li>

                <li class="nav-divider"></li>

                <li class="dropdown-header">Python</li>

                <li><a href="#">Python</a></li>

                <li><a href="#">Python</a></li>

                <li><a href="#">Python</a></li>

                <li><a href="#">Python</a></li>

            </ul>

        </li>

        <li><a href="#">联系我们</a></li>

        <li><a href="#">关于我们</a></li>

        <li><a href="#">注册</a></li>

        <li><a href="#">登陆</a></li>

        <form role="from" class="navbar-form navbar-right">

            <div class="form-group">

                <input type="text" class="form-control" placeholder="请输入..." />

            </div>

            <button class="btn btn-default">

                搜索

                <span class="glyphicon glyphicon-search"></span>

            </button>

        </form>

    </ul>

    </div>

</div>