Checkboxes not working PHP

I have a problem in the WP-Pro-Quiz plugin for WordPress. There are "Single Answer Options" that are visible, but not selectable. I need these options, I was thinking I might be able to get the checkboxes to function and in turn get the result I need in my quiz.

What is causing these checkboxes to be "Greyed Out"?

       <?php
}
private function singleChoiceOptions($data)
 {
    $single = $data[0];
    ?>
    <div class="postbox" id="singleChoiceOptions">
        <h3 class="hndle"><?php _e('Single choice options', 'wp-pro-quiz'); ?></h3>

        <div class="inside">
            <p class="description">
                <?php _e('If "Different points for each answer" is activated, you can activate a special mode.<br> This changes the calculation of the points',
                    'wp-pro-quiz'); ?>
            </p>
            <label>
                <input type="checkbox" name="answerPointsDiffModusActivated"
                       value="1" <?php $this->checked($this->question->isAnswerPointsDiffModusActivated()); ?>>
                <?php _e('Different points - modus 2 activate', 'wp-pro-quiz'); ?>
            </label>
            <br><br>

            <p class="description">
                <?php _e('Disables the distinction between correct and incorrect.', 'wp-pro-quiz'); ?><br>
            </p>
            <label>
                <input type="checkbox" name="disableCorrect" disabled="enabled"
                       value="1" <?php $this->checked($this->question->isDisableCorrect()); ?>>
                <?php _e('Disable correct and incorrect.', 'wp-pro-quiz'); ?>
            </label>

            <div style="padding-top: 20px;">
                <a href="#" id="clickPointDia"><?php _e('Explanation of points calculation', 'wp-pro-quiz'); ?></a>
                <?php $this->answerPointDia(); ?>
            </div>
        </div>
    </div>

    <?php
}