Things like Hula hoops（呼啦圈）used to be very popular. Did you ever own any of these？If you didn't，don't feel too bad. They were all fads. A fad is something that becomes very_____among a large number of people，but only for a short time. Something can become a fad veryquickly，but can stop being popular just asquickly. _____it is no longer“cool”，a fad goes away. Anything can become a fad-fashion，food，music，technology，even language.

In the late 1970s，Erno Rubik，a professor was looking for a_____way to teach his students about 3D objects. He invented a six-color plastic object that would be called the Rubik's Cube（魔方）. The goal was to get each side of the cube a_____color. It was very challenging. It took a few years for the toy to become popular，but then_____，in 1982，it seemed everyone had one. People bought over a hundred million of the toys. There were 50 books available that year offering solutions. Then，just as suddenly as the craze（风尚）started，it_____. By 1983，people were not interested in the Rubik's Cube anymore，perhaps because so many people_____had one in their home.

In 2012，a South Korean musician named Psy released a song called“Gangnam（江南）Style”. The music video shows Psy pretending to horse-ride while he is dancing. In six months，it became the first YouTube video ever to reach a billion views. Six months after that，_____went to reach two billion views. The song and video started a worldwide_____craze. “Gangnam Style”had a huge influence on world popular culture. The former US President Barack Obama and UK Prime Minister David Cameron even______the dance. Then“Gangnam Style”became less and less popular.