function ac()
{
    var i;
    var date = new Date();
    var year = date.getFullYear();
    
    if(document.jinbang.year.options.length == 0)
    {
        for(i = 1900; i <= year + 1; i++){
            document.jinbang.year.options[i - 1900]=new Option(i,i);
        }
        document.jinbang.year.options[year - 1900].selected = true;
        document.jinbang.month.options[date.getMonth()].selected = true;
        document.jinbang.hour.options[date.getHours()].selected = true;
        document.jinbang.day.options[date.getDate() - 1].selected = true;
    }
    var md = 0;
    var l;

    year = parseInt(document.jinbang.year.value);
    var month = parseInt(document.jinbang.month.value);
    var day = parseInt(document.jinbang.day.value);

    switch(month) 
    { 
        case 1: 
        case 3: 
        case 5: 
        case 7: 
        case 8: 
        case 10: 
        case 12:
            md = 31; 
            break; 
        case 4: 
        case 6: 
        case 9: 
        case 11:
            md = 30; 
            break; 

        case 2: 
            if(year%4 == 0) 
            {
                md = 29; 
            }
            else {
                md = 28;
            }
           break;
    }
    
    while(document.jinbang.day.options.length != md) {
        l = document.jinbang.day.options.length;
        if(document.jinbang.day.options.length > md) {
            document.jinbang.day.options.remove(l -1)
        }
        else {
            document.jinbang.day.options[l]=new Option(l + 1,l + 1);
        }
    }
    
}