tl;dr: C.) to get rid of something unwanted.
Hello!
The correct answer is C.) to get rid of something unwanted.
In the passage, you can see that the villains were "imprisoned on the Isle of the Lost". This shows that they were not needed in the United Kingdom of Auradon, hence the answer "to get rid of something unwanted.
Hope this answer was helpful. Please correct me if I'm wrong. Have a great day!