The correct response is:
Both religions were widespread on the continent at different points in time. Islamic empires flourished in Spain under Islamic rule and during the Ottoman Empire. Christian kingdoms flourished across most of Europe apart from these areas and regained a foothold in Spain after the Reconquista.
This statement accurately reflects the historical growth of both Islam and Christianity in Europe between 300 and 1500 CE, noting the significant Islamic presence in regions such as Spain, as well as the dominance of Christianity across most of Europe during this time.