how can remove empty <li>??

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 html;

var correct = [];
var wrong = [];

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

function builtList(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 = parseInt(prompt(question));
  if (response === answer) {
    correctAnswers += 1;
    correct.push(question);
  } else {
    wrong.push(question);
  }
}

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