Ordered list items not appearing on the page

var questions = [
  ['How many states are in the United States?', 50],
  ['How many continents are there?', 7],
  ['How many legs does an insect have?', 6]
];
var correctAnswers = 0;
var question;
var answer;
var response;
var correct = [];
var wrong = [];

function print(message) {
  var outputDiv = document.getElementById('output');
  outputDiv.innerHTML = message;
}

function buildList( arr ) {
  var listHTML = '<ol>';
    for ( var i = 0; i < arr.length; i += 1) {
      listHTML += '<li>' + arr[i] + '</li>';
  }
  listHTML = '</ol>';
  return listHTML;
}

for (var i = 0; i < questions.length; i += 1) {
  question = questions[i][0];
  answer = questions[i][1];
  response = prompt(question);
  response = parseInt(response);
  if (response === answer) {
    correctAnswers += 1;
    correct.push(question);
  } else {
    wrong.push(question);
  }
}

html = 'You got ' + correctAnswers + ' question(s) right.';
html += '<h2> You got these questions correct:</h2>';
html += buildList(correct);
html += '<h2> You got these questions wrong:</h2>';
html += buildList(wrong);
print(html);