Remove item from dropdown list on page load (no jquery)

Answer 1

Since everyone else has proposed basically the same solution, here's a simpler solution if you have the benefit of only targeting modern browsers:

var el = document.querySelector('select[name=DD1] option[value=D]');
el.parentNode.removeChild(el);

Or, for every browser:

var el;
if(typeof document.querySelector == 'function') {
  el = document.querySelector('select[name=DD1] option[value=D]');
} else {
  for(var child in document.getElementById('DD1').childNodes) {
    if(child.textContent == 'D') {
      el = child;
      break;
    }
  }
}

el && el.parentNode.removeChild(el);