Bertha Jorkins useful to Voldemort in a sense that she gave him the information he used to form his plan.
Answer: Option D
Explanation:
Harry potter is a series of book written by a very well known writer J.K. Rowling. In one of the series name Harry potter and the Goblet of fire, Bertha Jorkins help Voldemort by giving him news about the Triwizard match.
Voldemort managed to break through her memory by using a powerful charm, so he could get some important information about the Triwizard Tournament which he used to try to kill Harry Potter.
This was one of the tournament that was being organised at Hogwarts. And by being a part of this tournament, it was a chance for Voldemort to kill Harry Potter.