Attempt at Quiz. Suggestions and critics welcome! :)

//Defining variables & constants
/*******************************/
const startButton = document.getElementById('start');
const displayQuestion = document.getElementById('question');
const choice0 = document.getElementById('choice0');
const choice1 = document.getElementById('choice1');
const buttonGuess0 = document.getElementById('guess0');
const buttonGuess1 = document.getElementById('guess1');
const progress = document.getElementById('progress');
const nextQuestion = document.getElementById('next');
const viewScore = document.getElementById('score');
var currentQuestion = 0;
var score = 0;
var fug = new Questions("What was Ian Mackaye's first band?", "Minor Threat", "Black Flag");
var built = new Questions('Which of these is a cult record by "Built to Spill?"', "Keep it like a Secret", "At Action Park");
var myQuiz = new Quiz();
/*******************/
//Defining Function
/*******************/

//Making sure the choices are displayed randomly//
/************************************************/
function random() {
  if (Math.floor(Math.random() * 2 < 1)) {
    return choice0;
  }else {
    return choice1;
  }
};
/************************/
//Constructor functions//
/************************/
function Questions(question, option1, option2) {
  this.question = question;
  this.option1 = option1;
  this.option2 = option2;
}

function Quiz() {
  this.questionsList = [];
}

Quiz.prototype.add = function(question, option1, option2) {
  this.questionsList.push(question);
};

myQuiz.add(fug);
myQuiz.add(built);
/*************************/
//Interaction functions//
/***********************/
function removeHtml() {
  displayQuestion.innerHTML = "";
  choice0.innerHTML = "";
  choice1.innerHTML = "";
}

function displayQuestions() {
  removeHtml();
  displayQuestion.className = "";
  displayQuestion.innerHTML = myQuiz.questionsList[currentQuestion].question;
  random().innerHTML = myQuiz.questionsList[currentQuestion].option1;
  if(choice0.innerHTML === "") {
    choice0.innerHTML = myQuiz.questionsList[currentQuestion].option2;
  }else{
    choice1.innerHTML = myQuiz.questionsList[currentQuestion].option2;
  }
  progress.innerHTML = "Question " + (currentQuestion + 1) + " of " + myQuiz.questionsList.length;
  currentQuestion++;
}

function resetClass() {
  choice0.className = "";
  choice1.className = "";
}

function hideDisplay() {
  choice0.style.display = 'none';
  choice1.style.display = 'none';
  progress.style.display = 'none';
  guess0.style.display = 'none';
  guess1.style.display = 'none';
}

function showDisplay() {
  choice0.style.display = 'block';
  choice1.style.display = 'block';
  progress.style.display = 'block';
}

function keepScore() {
  if (choice0.className === "selected" && choice0.innerHTML === myQuiz.questionsList[currentQuestion - 1].option1){
    score++;
  }
  if (choice1.className === "selected" && choice1.innerHTML === myQuiz.questionsList[currentQuestion - 1].option1){
    score++;
  }
}

function displayScore() {
  if (score === 0) {
    displayQuestion.innerHTML = "You suck...You did not get 1 question right.";
  }else if (score === 1){
    displayQuestion.innerHTML = "You only got 1 question right.";
  } else if (score === 2){
    displayQuestion.innerHTML = "Well done!! You got both questions right!";
    displayQuestion.className = "winner";
  }
}
/**********************************/
//Event Listeners/ DOM Manipulation
/**********************************/
nextQuestion.style.display = 'none';
buttonGuess0.style.display = 'none';
buttonGuess1.style.display = 'none';
viewScore.style.display = 'none';

startButton.addEventListener('click', function() {
  score = 0;
  displayQuestions();
  startButton.style.display = 'none';
  nextQuestion.style.display = 'block';
  buttonGuess0.style.display = 'block';
  buttonGuess1.style.display = 'block';
  showDisplay();
});

nextQuestion.addEventListener('click', function() {
  keepScore();
  resetClass();
  displayQuestions();
  if (currentQuestion === myQuiz.questionsList.length) {
    nextQuestion.style.display = 'none';
    viewScore.style.display = 'block';
  }
});

buttonGuess0.addEventListener('click', function() {
  if (choice1.className = "selected") {
    choice1.className = "";
    choice0.className = "selected";
  }
});

buttonGuess1.addEventListener('click', function() {
  if (choice0.className = "selected") {
    choice0.className = "";
    choice1.className = "selected";
  }
});

viewScore.addEventListener('click', function() {
  keepScore();
  hideDisplay();
  displayScore();
  viewScore.style.display = 'none';
  startButton.innerHTML = "Restart Quiz";
  startButton.style.display = 'block';
  currentQuestion = 0;
  resetClass();
});