Task: Question Answering
Input (English): Passage: In Bedrock, Slate International's vice president Cliff Vandercave and his secretary Miss Stone discuss their plan to swindle the company of its vast fortune and flee. As part of the plan, they would need one of the employees to be the scapegoat. Meanwhile, Fred Flintstone loans his best friend and neighbor Barney Rubble money so that he and his wife Betty can adopt a child. The agency pairs them up with a child named Bamm-Bamm, who can only pronounce his own name. Although Bamm-Bamm is initially difficult to control due to being raised by mastodons, and thus has super strength, he eventually warms up to his new family. Barney vows to repay his friend Fred for his debt of gratitude. Despite his mother-in-law Pearl Slaghoople's objections, Fred's wife Wilma remains supportive of Fred's decision to help Barney. Fred promises he will prove himself to her one day. 
Question: Who does Fred promise to prove himself to?
Output (English): Pearl Slaghoople.