Why is only the first letter of each question is displayed...?

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>';  // ol, not sure why this isn't visible but it's in the original code
  for ( var i = 0; i < arr.length; i += 1 ) {
    listHTML += '<li>' + arr[i][0] + '</li>';
  }
  listHTML += '</ol>'; // ol, not sure why this isn't visible but it's in the original code
  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);