Undefined global variables

I know that this question may be a "dumb" one but just forgive me for this :( I was doing a quiz-time application but just got a problem :( my two global variable are not defined which are "score" and "solvedQuestions" although there's no variable has the same name... here's the code

     var score = 0;
 var solvedQuestions = 0;
 //prototype
 function Question(quest, option1, option2, option3, correct) {
     this.quest = quest;
     this.option1 = option1;
     this.option2 = option2;
     this.option3 = option3;
     this.correct = correct;

 }
 //creating questions
 var question1 = new Question("1 + 1", 2, 3, 3, 1);
 var question2 = new Question("2 + 2", 4, 3, 3, 2);
 var question3 = new Question("3 + 3", 6, 3, 3, 3);
 var question4 = new Question("4 + 4", 8, 3, 3, 1);
 var question5 = new Question("5 + 5", 10, 3, 3, 2);
 var question6 = new Question("6 + 6", 12, 3, 3, 3);
 //the questions array
 var questions = [];
 //pushing questions to array
 questions.push(question1);
 questions.push(question2);
 questions.push(question3);
 questions.push(question4);
 questions.push(question5);
 questions.push(question6);
 var randomQuestionIndex = Math.floor(Math.random() * 6);
 // Builds the questions in the first loop
 function QuestionPre() {
     randomQuestionIndex = Math.floor(Math.random() * 6);
     document.querySelector("#question").innerHTML = questions[randomQuestionIndex].quest;
     document.querySelector(".option-1").innerHTML = questions[randomQuestionIndex].option1;
     document.querySelector(".option-2").innerHTML = questions[randomQuestionIndex].option2;
     document.querySelector(".option-3").innerHTML = questions[randomQuestionIndex].option3;

 }
 QuestionPre();
 // resets them after answering
 function QuestionReset() {
     randomQuestionIndex = Math.floor(Math.random() * 6);
     document.querySelector("#question").innerHTML = questions[randomQuestionIndex].quest;
     document.querySelector(".option-1").innerHTML = questions[randomQuestionIndex].option1;
     document.querySelector(".option-2").innerHTML = questions[randomQuestionIndex].option2;
     document.querySelector(".option-3").innerHTML = questions[randomQuestionIndex].option3;
 }
 document.querySelector(".lock-btn").addEventListener("click", function() {
     if (document.querySelector(".option-" + questions[randomQuestionIndex].correct + "-check").checked === true) {
         alert("Correct, such a Genius !");
         score = score + 1;
         QuestionReset();
         solvedQuestions = solvedQuestions + 1;
     } else {
         alert("Wrong mate, such a bad luck !");
         randomQuestionIndex = Math.floor(Math.random() * 6);
         QuestionReset();
         solvedQuestions = solvedQuestions + 1;



     }
     // End the Questions
     if (solvedQuestions >= 6) {
         window.location.href = "score.html";
         document.querySelector(".score-preview").textContent = score;
     }

 });

Thanks in advance.