I'm constructing a quiz application and am having trouble verifying whether or not user answers are correct. The quiz contains 10 questions, and uses radio buttons (multiple choice) to get answers from the user. For some of thequestions, none of the answers register as correct. For some of the other questions, all of the answers register as correct.

Here is a JS Fiddle with all of the code: http://jsfiddle.net/MCjna/

The counter below the quotation indicates whether or not you got the question right (if you're right, the number increases by 1).

Each question has its own 'questionClass,' outlined like so:
Code:
function questionClass (q, a1, a2, a3, a4, n, c) {
this.question = q;
this.answer1 = a1;
this.answer2 = a2;
this.answer3 = a3;
this.answer4 = a4;
this.number = n;
this.correct = c;
Each of the question classes are created with the following formula:
Code:
var questionOne = new questionClass("question", 'answer1','answer2','answer3','answer4', number, 'correct');
questions.push(questionOne);
The function for verifying whether or not the user got the correct answer is here:
Code:
this.checkAnswer=checkAnswer;
    function checkAnswer() {

    if ($('input:radio[name=" ' + this.number + ' "]:checked').val() == this.correct) {
        score++;
    }
    else if ($('input:radio[name=" ' + this.number + ' "]:checked').val() == this.correct) {
        score++;
    }
    else if ($('input[id=" ' + this.answer3 + ' "]:checked') && (this.answer3 == this.correct)) {
        score++;
    }
    else if ($('input[id=" ' + this.answer4 + ' "]:checked') && (this.answer4 == this.correct)) {
        score++;
    }
    else {
        console.log("you got the wrong answer");
    }

}
The function for moving between questions is as follows:
Code:
$("#continue").click(function(){
    counter++;

    if (counter == 1) {
        questions[x].display();
    }
    else if ((counter >= 1) && (counter <= 10)) {
        if (questions[x].isSelected()) {
            $('.warning').html("");
            questions[x].checkAnswer();
            $('.score').html("<p>Your score is " + score + " out of 10</p>");
            x++;
                if (x < 10){
                    questions[x].display();
                }
        }
    }
    else if ((counter >= 11) && (!questions[x].isSelected())) {
        return;
    }
    else {
        $('.warning').html("");
        questions[x].checkAnswer();
        $('.score').empty();
        $('#container').html('<h1>You scored ' + score + ' out of 10.</h1></br>');
        $('#container').append('<input type="button" id="tryAgain" value="Try Again!">');

    }
});