Javascript I made, plez dont open

function script()
{
x=document.getElementById("div.lab-frame.mode-practice");
y=document.getElementById("div.lab-frame.mode-practice");
z=document.getElementById("div.lab-frame.mode-practice");
a=document.getElementById("div.lab-frame.mode-practice");
b=document.getElementById("div.lab-frame.mode-practice");
c=document.getElementById("div.lab-frame.mode-practice");
x.innerHTML="MC1";
y.innerHTML="MC1";
z.innerHTML="MC1";
a.innerHTML="MC1";
b.innerHTML="MC1";
c.innerHTML="MC1";
}

BC = x.innerHTML