Answer:
Igraine and Merlin's secret was that Arthur was king's Uther son and heir to the throne.
D)
Step-by-step explanation:
The reason Edith. Also, that he says after Arthur takes the sword from the stone that he is the rightful heir for the Kingdom and that the act of taking out the sword from the stone is a second fact apart from his knowledge of Arthur's legitimacy and origin. But, considering people were not going to take that as truth, only taking the sword out would provide them the evidence required to believe Arthur was the heir for the throne.