The most accurate response to compare the growth of Islam and Christianity in Europe between 300 and 1500 CE 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 option correctly reflects the historical context, noting that Islam had a significant presence in parts of Europe, particularly in the Iberian Peninsula, while Christianity dominated in most of the rest of Europe during this period. The Reconquista was a critical event that saw the Christian kingdoms of Spain reclaiming territory from Muslim rule. Additionally, the rise of the Ottoman Empire later in this period brought Islam back into significant influence in southeastern Europe.