if statement within the for loop is not incrementing the "correctAnswers" variable - even though syntax looks correct

var quizQuestions = [
  [ 'What is the color of the sun?' , 'Yellow' ] ,
  [ 'What is the color of the grass?' , 'Green' ] ,
  [ 'What is the color of the sky?' , 'Blue'] ,
];

  var correctAnswers = 0;
  var question;
  var answer;
  var response;
  var html;

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

// Ask the questions

  for (var i = 0; i < quizQuestions.length; i += 1) {
    question = quizQuestions[i][0];
    answer = quizQuestions[i][1];
    response = prompt(question).toLowerCase();

  if (response === answer) {
    correctAnswers += 1;
  }

}

html = "You got " + correctAnswers + " question(s) correct.";
print(html);