restricting the number of questions
function klick(el) {
  g_count++;
  ...
function get_pic() {
  clear();
  if (g_count<g_questions) {
  ...
  }
}
Adding scoring

Make sure that you add var g_score=0; to your globals.js.

function klick(el) {
  g_count++;
  var el_answer=document.getElementById(g_answer_id);
  el_answer.style.backgroundColor='palegreen';
  var id=el.id;
  if (id!=g_answer_id) {
    el.style.backgroundColor='red';
  } else {
    g_score++;
  }
  var el_score=document.getElementById('score');
  el_score.textContent='Score: '+g_score+' / '+g_count;
  setTimeout(get_pic,3000);
}