Как сделать синхронизацию двух полей select?

var opt = document.getElementById("options"); 
document.getElementById("var_numbers").addEventListener("change", function() { 
  var currentVal = this.value; 
  if (currentVal == 0) { 
    for (var i = 0; i < opt.children.length; i++) { 
      opt.children[i].disabled = true; 
    } 
    opt.children[opt.children.length - 1].disabled = false; 
    opt.children[opt.children.length - 1].selected = true; 
  } else { 
    for (var i = 0; i < opt.children.length; i++) { 
      if (i < currentVal) { 
        opt.children[i].disabled = false; 
      } else { 
        opt.children[i].disabled = true; 
      } 
    } 
    opt.children[0].selected = true; 
  } 
});

<select id="var_numbers"> 
  <option value="1" selected>Вариант 1</option> 
  <option value="2">Вариант 2</option> 
  <option value="3">Вариант 3</option> 
  <option value="0">Без вариантов</option> 
</select> 
 
 
<select id="options"> 
  <option value="1" selected>option 1</option> 
  <option value="2" disabled>option 2</option> 
  <option value="3" disabled>option 3</option> 
  <option value="0" disabled>No options</option> 
</select>