Quiz with select form JS

how can i make it take the correct answers from the select and add them to the correct. If answered correctly in the select to write “You got 7 correct”.

Now it works only for radio button and for the text …

I make for cycle but i dont know how to add the check of if to work properly

var qs_select= document.getElementsByTagName("select");
    var num_select_questions=qs_select.length/1;
    var ans_select=[2,1];

for(let i=0; i<num_select_questions; i++){
			var left=qs_select[i];
			var right= qs_select[i+1];
			if(left.selectedIndex==ans_select[i] && 
				right.selectedIndex==ans_select[i+1])sum +=1;
		}

The code:

<!DOCTYPE html>
<html>
<head>

<title>Document</title>
<link href="https://fonts.googleapis.com/css?family=Lato" rel="stylesheet">
</head>

<body>

<form id = "quiz" name = "quiz">

<p class = "questions">"Who is write Elegiya" </p>
<input id = "textbox" type = "text" name = "question1">

<p class = "questions">Real name of Elin Pelin?</p>
<input id = "textbox" type = "text" name = "question5">

<p class = "questions">In whitch age Hristo Botev died?</p>
<input id = "textbox" type = "text" name = "question6">

<p class = "questions">Which Bulgarian rivers spring from the Rila mountain?</p>
<input type = "radio" id = "mc" name = "question2" value = "Iskar and Maritsa">Iskar and Maritsa<br>
<input type = "radio" id = "mc" name = "question2" value = "Augusta and Yantra">Augusta and Yantra<br>

<p class = "questions"> Which was the capital of Bulgaria during the reign of Khan Krum</p>

<input type = "radio" id = "mc" name = "question3" value = "Turnovo">Turnovo<br>
<input type = "radio" id = "mc" name = "question3" value = "Pliska">Pliska<br>

<p class = "questions">Which literary school was founded by Clement, the pupil of Cyril and Methodius?</p>
<input type = "radio" id = "mc" name = "question4" value = "Turnovska">Turnovska<br>
<input type = "radio" id = "mc" name = "question4" value = "Ohrid">Ohrid<br>

<p>Select your matching items from the two adjacent lists</p>
<fieldset  id="select">
	<div>
        <select size="3">	
            <option>Atanas Dalchev</option>
            <option>Hristo Botev</option>
			<option>Geo Milev</option>
		</select>
		<select size="3">	
            <option>To Chicago and Back</option>
            <option>September</option>
			<option>Albena</option>
		</select>
</fieldset>


<input id = "button" type = "button" value = "The moment of truth ... !" onclick = "check();">


</form>

<div id = "after_submit">
<p id = "number_correct"></p>
<p id = "message"></p>
<img id = "picture">
</div>

<script>
   
   function check(){

    var question1 = document.quiz.question1.value;
    var question2 = document.quiz.question2.value;
    var question3 = document.quiz.question3.value;
    var question4 = document.quiz.question4.value;
    var question5 = document.quiz.question5.value;
    var question6 = document.quiz.question6.value;
    var correct = 0;

	
    if (question1 == "Hristo Botev"){
        correct++;
    }
    if (question5 == "Dimitur Stoyanov"){
        correct++;
    }
    if (question6 == "28"){
        correct++
    }
    if (question2 == "Iskar and Maritsa"){
        correct++;
    }	
    if (question3 == "Pliska"){
        correct++;
    }
    if (question4 == "Oxrid"){
        correct++;
    }

var pictures = ["img/win.gif", "img/meh.jpeg", "img/lose.gif"];
var messages = ["Great job!", "That's just okay", "You really need to do better"];
var score;

if (correct == 0) {
    score = 2;
}

if (correct > 0 && correct < 6) {
    score = 1;
}

if (correct == 6) {
    score = 0;
}

// for select 
var qs_select= document.getElementsByTagName("select");
    var num_select_questions=qs_select.length/1;
    var ans_select=[2,1];

for(let i=0; i<num_select_questions; i++){
			var left=qs_select[i];
			var right= qs_select[i+1];
			if(left.selectedIndex==ans_select[i] && 
				right.selectedIndex==ans_select[i+1])correct+=1;
		}

document.getElementById("after_submit").style.visibility = "visible";

document.getElementById("message").innerHTML = messages[score];
document.getElementById("number_correct").innerHTML = "You got " + correct + " correct.";
document.getElementById("picture").src = pictures[score];
}

</script>

</body>
</html>