7．
It's not a chocolate coin wrapped in gold foil，people．That's actual metal that composes that Olympic medal，so why do athletes bite them？There's actually a few reasons，but the most obvious is that it's a pose photographers really，really like to capture．
"It's become an obsession （迷恋） with the photographers，"David Wallechinsky，the president of the International Society of Olympic Historians and co-author of"The Complete Book of the Olympics"told CNN in 2012．"I think they look at it as an iconic（偶像的） shot，as something that you can probably sell．I don't think it's something the athletes would probably do on their own．"
Biting down on a piece of metal is more likely something someone might have done during the Gold Rush to test whether the shiny golden rock they just panned （淘洗） for was actually pyrite （硫化金） or fool's gold．Human teeth are harder than gold but softer than pyrite，according to the Mohs Hardness Scale，which categorizes how easily minerals scratch．This means a quick bite to real gold would actually leave an indentation（缺口，凹进）．A hard chew of pyrite，meanwhile，might damage your teeth．
The practice also once served to see whether coins were solid gold or just gold-plated （镀金） over a cheaper metal，Today I Found Out explains．With that in mind，it's likely that Old West/pirate lore （传说） led to someone once biting their Olympic medal in a spontaneous （自动的，自发的），"Is this real life？"moment，and the photographers thought it was cute．Because if someone really was hoping to discover whether that gold medal is pure gold，their smiles would quickly fade．
Olympic gold medals are actually just 1.34 percent gold．The rest is silver．And much of it is recycled silver this time around，which makes the 2016 Rio medals"the most sustainable ever made，"according to Forbes magazine contributor Anthony DeMarco （via ABC News）．DeMarco says the materials that make up a"gold"medal are worth﹩564．
Winning athletes would be better served to make sure the checks they receive for coming out on top don't bounce．Along with their gold medals，Olympic winners get﹩25，000 prizes．
28．Your teeth won't be damaged according to the passage when you biteB．
A．pyrite B．gold C．fool's gold D．gold-plated metals
29．Which of the following statements is TRUE about athletes biting Olympic medals？D
A．The photos of biting medals sell well for athletes．
B．Athletes are keen on biting medals when photographed．
C．Olympic medals are chocolate coins wrapped in gold foil．
D．Athletes are required by photographers to bite medals．
30．The underlined"solid"in Paragraph 4 is closest in meaning toA．
A．pure B．hard C．strong D．fake
31．From the last three paragraphs，we can infer thatC．
A．Old West pirate judged gold by biting it
B．Olympic gold medals are made of a little gold
C．it's winning not pure gold medals that make athletes smile
D．photographers thought that athletes'biting gold medals was cute．
