I tried to discourage him, but he persisted _______ revealing the secret of his son.
Answer Details
The option that best completes the sentence is "in".
"I tried to discourage him, but he persisted in revealing the secret of his son."
The word "persisted" implies that the person continued to do something despite opposition or discouragement. In this case, the person persisted in revealing the secret of his son, which means that he continued to do so despite being discouraged.
The preposition "in" is used to indicate that the person persisted in a particular action or behavior. In this case, the person persisted in revealing the secret. Therefore, the correct option is "in".