My quiz questions remain undefined and I can't figure out why.

I've checked the console and there aren't any errors there.. I've looked at other questions and reviewed the video several times to see if it matches my code... I'm really stuck and can't figure out what happened. When viewing the page, it'll ask the quiz questions it's supposed to and will let the user know how many questions they answered correctly and incorrectly, but the questions it's supposed to list just says undefined. If anyone can look at my code and let me know where I messed up, I would really appreciate it. Thanks in advance!!

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 buildList(arr) { var listHTML = '<ol>'; for( i = 0; i < arr.length; i += 1); { listHTML += '<li> ' + arr.length[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 incorrect: " + "</h2>"; html += buildList(wrong);

print(html);