function On(id_){
 document.getElementById(id_).style.display='block'
}
function Off(id_){
 document.getElementById(id_).style.display='none'
}

function changeVisibility(id_){
if(document.getElementById(id_).style.display=='block'){
 Off(id_);
}
else{
 On(id_);
}
}

function Step1(){
 changeVisibility('div1');
 changeVisibility('div1d');
 changeVisibility('div21');
 changeVisibility('div22');
}
function Step21(){
 changeVisibility('div1');
 changeVisibility('div1d');
 changeVisibility('div21');
 changeVisibility('div22');
}

function Step20(){
 changeVisibility('div1');
 changeVisibility('div1d');
 changeVisibility('div21');
 changeVisibility('div22');
}

function Step22(){
 changeVisibility('div21');
 changeVisibility('div21d');
 changeVisibility('div22');
 changeVisibility('div22d');
 changeVisibility('div3');
}


function Ok21(){
 changeVisibility('div_common');
 changeVisibility('div_answer');

}

function Step3(){
 changeVisibility('div3');
 changeVisibility('div4');
}
function Step42(){
 changeVisibility('div4');
 changeVisibility('div_common');
 changeVisibility('div_answer');
}
function Step41(){
 changeVisibility('div41');
 changeVisibility('div5');
}

function StepSerious(){
 changeVisibility('div4');
 changeVisibility('div0');
}