The correct answer is A. good.
A grotesque palace is a palace that is ugly and unpleasant to look at. It may be decorated in a way that is considered to be tasteless or offensive. It may also be in a state of disrepair or neglect.
A good palace, on the other hand, is a palace that is beautiful and impressive. It may be decorated in a way that is considered to be tasteful and elegant. It may also be in a state of good repair and well-maintained.
The other options are not correct because they do not accurately describe a grotesque palace.
B. decent: A decent palace is a palace that is of a good standard. It may not be as beautiful or impressive as a good palace, but it is still a palace that is worth visiting.
C. filthy: A filthy palace is a palace that is dirty and unkempt. It may be covered in dust and cobwebs, and it may have a strong smell of mildew.
D. congruous: A congruous palace is a palace that is in harmony with its surroundings. It may be built in a style that is similar to the other buildings in the area, and it may be decorated in a way that reflects the local culture.