// Add another drop down to the visual editor
add_filter( 'mce_buttons_2', 'fb_mce_editor_buttons' );
function fb_mce_editor_buttons( $buttons ) {

    array_unshift( $buttons, 'styleselect' );
    return $buttons;
}
add_filter( 'tiny_mce_before_init', 'fb_mce_before_init' );
function fb_mce_before_init( $settings ) {
    $style_formats = array(
        array(
            'title' => 'Question',
            'selector' => 'p',
            'classes' => 'question'
        ),
        array(
            'title' => 'Answer',
            'selector' => 'p',
            'classes' => 'answer',
        )
    );
    $settings['style_formats'] = json_encode( $style_formats );
    return $settings;
}