The correct answer is A. Beautiful
Step-by-step explanation:
In the sentence "Once a fair and stately palace" the word "fair" along with the word "stately" that means impressive or majestic are used to describe a palace. Considering the word "stately" has a positive connotation and refers to the palace being attractive it is likely the word "fair" has a similar positive connotation. According to this, the meaning of the word fair in this line is "beautiful" considering this meaning as the one of "stately" defines the palace positively. Also, others such as destructive, unplaned or mysterious are not directly related to the word "fair".