var menu = document.getElementById('menu');
        var span = document.getElementById('span');
        menu.onclick=function(){
            switch(menu.value){
                 case 'fruit':
                span.innerHTML = '苹果、香蕉、西瓜、鸭梨、橙子';
                break;
                
                case 'cake':
                span.innerHTML = '慕斯、奶酪、海绵、巧克力';
                break;
                
                case 'nuts':
                span.innerHTML = '巴旦木、碧根果、开心果、核桃、腰果';
                break;
                
                default : span.innerHTML='';
            }
        }