السلام عليكم و رحمة الله و بركاته
ارى انه لابد من وضع نقطة بعد written و فى هذه الحالة الاجابة الافضل ستكون had
او وضع فاصلة بعد written و فى هذه الحالة الاجابة having
After he had written the articles
Having written the articles
The articles having been written