Second job

<! DOCTYPE HTML> 
<HTML> 
<head> 
	<title> completion of City three linkage (including Hunan), with code and renderings. </ title> 
</ head> 
<body> 
 <SELECT ID = "Province"> 
   <Option value = "-. 1"> select </ Option> 
 </ SELECT> 
 <SELECT ID = "City"> </ SELECT> 
 <SELECT ID = "Country"> </ SELECT> 
 <Script type = "text / JavaScript"> 
   var provinceArr = [ "Shanghai", "Jiangsu ',' Hebei ',' Hunan ']; 
   var cityArr = [ 
                  [' Shanghai City '], 
                  [' Suzhou ',' Nanjing ',' Yangzhou '], 
                  [' Shijiazhuang ',' Qinhuangdao ',' Zhangjiakou '], 
                     [ 
                      [ 'Huqiu', 'Wu area', 'city phase', 'Suzhou area', 'region Wujiang'], 
                      [ 'Xuanwu', 'Qinhuai area', 'Jianye', 'Drum area ',' pukou '], 
                      [' Hanjiang ',' Guangling ',' region jiangdu '] 
                     ], 
                     [ 
                      [' Chang'an ',' west region ',' Xinhua area ',' Jingxing mining '], 
                      [ 'harbor area', 'region Shanhaiguan', 'Beidaihe area', 'region funing'], 
                      [ 'region east', 'west region', 'Xuanhua area', 'region Xiahuayuan'] 
                     ], 
                     [ 
                      [ 'Hibiscus area', 'region Yuelu', 'Tianxin' 'Kaifu District '], 
                      [' Hetang ',' Lusong ',' Shifeng ',' Tianyuan '], 
                      [' Yuhu ',' Yuetang '] 
                     ] 
                    ]; 
    function creatOption (obj, Data) { 
    	for (var Data in I ) {
    		var op = new Option(data[i],i);
    		obj.options.add(op);
    	}
    }
    var province = document.getElementById('province');
    creatOption(province,provinceArr);   

    var city = document.getElementById("city");
    province.onchange = function(){
    	city.options.length = 0;
    	creatOption(city,cityArr[province.value]);
    	if(province.value >= 0){
    		city.onchange();
    	}else{
    		country.options.length = 0;
    	}
    };

    var country = document.getElementById("country");
    city.onchange = function(){
    	country.options.length = 0;
    	creatOption(country,countryArr[province.value][city.value]);
    };              
 </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    
</head>
<body>
    
    <script>
        var arr = [1,2,3,4,2,5,6,2,7,2];
        var arr2 = arr.filter(function(item){
            if(item != 2){
                return true
            }
        })
        console.log(arr2)
    </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        #div{
            width: 400px;
            height: 400px;
            background-color:#ccc;
            margin: 100px auto;
        }
        .add{
            border: 10px double red;
        }
    </style>
</head>
<body>
    <div id="div"></div>
    <input type="button" value="change" id="change">
    <script>
        var btn = document.getElementById('change');
        var div = document.getElementById('div')
        btn.onclick = function(){
            div.classList.add('add')
        }
    </script>
</body>
</html>

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