document.feedback.platform.options.length=0;
document.feedback.platform.options[0]=new Option('--choose platform--','---');
//s='';
//s='<select name="platform">';
for(i=1;i<=a.length;i++){
    document.feedback.platform.options[i]=new Option(a[i-1][0],a[i-1][0]);
}//for i

document.feedback.platform.options[1].selected = true;
select_platform(document.feedback.platform.options[1]);