var   A=document.getElementsByClassName("a1")
        for (let i = 0; i <A .length; i++) {
         A [i] .onclick=function (){
          for( x=0;x<A.length;x++   ){
            A[x].style.background="url(0.png)"
            for (let j = 0; j< i+1; j++) {
              A[j] .style.background="url(1.png)"
            }


          }
         }
        }