String getType(Object obj) {
    if (obj instanceof List<object>) { return 'List'; }
    if (obj instanceof SelectOption) { return 'SelectOption'; }
    return '';
}

Object filterResponse(Object obj) {
    List<string> optionList = new List<string>();
    if (getType(obj).equals('List')) {

        List<object> objectList = (List<object>) obj;

        if (objectList.size() <= 0) { return obj; }

        if (getType(objectList.get(0)).equals('SelectOption')) {
            for(Object option: objectList) {
                SelectOption selectOption = (SelectOption) option;
                optionList.add(selectOption.getValue());
            }
            return optionList;
        }
        else {
            return obj;
        }
    }
    return obj;
}