Asks questions twice (6 total dialog boxes), but only reports 3 answers. Why is is prompting a second time?

//variable to collect users correct and wrong answers
var correctAnswers = 0 
var wrongAnswers = 0

//array of questions and answers
var questions = [
 [ 'What color is the sky?', 'blue' ],
 [ 'What color is the grass?', 'green' ],
 [ 'What color is the dirt?', 'brown' ]
]

//to ask user each question and store the answer
var questionOne = prompt( questions[0][0] );
var questionTwo = prompt( questions[1][0] );
var questionThree = prompt( questions[2][0] );

//to determine if the answer is correct
var question
var answer
var response
var HTML

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

//display score
HTML = "You got " + correctAnswers + " correct and " + wrongAnswers + " incorrect."
print(HTML);

function print(message) {
  document.write(message);
}