function checkForm(f) {
  if(f.email.value.length==0) {
    alert("Please enter an email address");
    return false;
  }
  if(f.ctr.value.length<6) {
    alert("The password should have at least 6 characters");
    return false;
  }
  if(f.ctr.value!=f.ctr2.value) {
    alert("The passwords don't match");
    return false;
  }

  if(!f.chk1.checked || !f.chk2.checked || !f.chk3.checked) {
    alert("You must agree to all conditions to sign up.");
    return false;
  }
  return true;
}