Final answer:
During the reign of absolutism in France, the Huguenots, who were French Protestants, were the religious group that faced severe persecution, notably during the St. Bartholomew's Day Massacre of 1572. The option (D) is correct.
Step-by-step explanation:
During the reign of absolutism in France, the religious group that was persecuted severely was the Huguenots. The Huguenots, who were French Protestants influenced by John Calvin, faced severe oppression and violence, most notably during the St. Bartholomew's Day Massacre of 1572. This tragic event started as targeted assassinations and escalated to mob violence, resulting in the deaths of thousands of Huguenots. It's a stark reminder of the religious intolerance that was rampant during the sixteenth and seventeenth centuries in Europe.
The persecution experienced by the Huguenots reflects the broader pattern of religious conflicts post-Reformation. In France, this intensified during the Wars of Religion and only subsided with the Edict of Nantes in 1598, which granted the Huguenots rights to worship, though Catholicism remained the official religion of France. Therefore, option (D) is correct.