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Question

here is my code:

Answer 1

as a side issue you dont need the style.visibility... line

one more thing:

Typically, its better to add event listeners using the attachEvent or addEventListener methods (allows more control, and multiple listeners for one action) like this:

function addEvent(el, eType, fn, uC) {
  if (el.addEventListener) {
    el.addEventListener(eType, fn, uC);
    return true;
  } 
  else if (el.attachEvent) {
    return el.attachEvent('on' + eType, fn);
  }
  else {
    el['on' + eType] = fn;
  }
}

and then just use

addEvent(
    document.getElementById("radio1"),
    "change",
    function(){
      if(this.checked == true){
            document.getElementById("list1").style.display = "none";
      }
    },
    false);

This is both cross-browser and better practice