Answer:
A medal and a phtograph Gatsby shows him make Gatsby's story convincing to Nick.
Explanation:
"The Great Gatsby" is a novel by author F. Scott Fitzgerald about the American dream and the rotten American society. Gatsby, a millionaire who attracts hundreds of people into his mansion by throwing grand parties, is a mystery to all. Incredible stories are told about his past, some of them even claim him to be a criminal.
Gatsby befriends Nick, the story's narrator. He's desperate to get the love of his life back, Nick's cousin Daisy. So he decides to make Nick his new best friend and to convince him that he - Gatsby - comes from a wealthy, cultured family/background. While driving, Gatsby tells Nick absurd stories about how his whole family died and he inherited their money. He also states he lived in Europe, collecting jewels, hunting big game, and painting. Nick has a hard time keeping himself from laughing at all this absurdity until Gatsby shows him a medal won at the war and a photo of himself at Oxford. Note the excerpt below:
He reached in his pocket, and a piece of metal, slung on a ribbon, fell into my palm.
"That's the one from Montenegro."
To my astonishment, the thing had an authentic look.
[...]
"Here is another thing I always carry. A souvenir of Oxford days. It was taken in Trinity Quad - the man on my left is now the Earl of Dorcaster."
It was a photograph of half a dozen young men in blazers [...] There was Gatsby, looking a little, not much, younger - with a cricket bat in his hand.
Then it was all true.
