Though she is already one of the most famous pop stars of the 21st century, you've probably never heard of a 25-year-old singer, song writer named Stefani Germanotta --- but that's only because almost everyone knows her by her stage name, Lady Gaga. Born in New York City in 1986, Lady Gaga enjoyed music, singing and dancing from an early age: she started playing the piano when only four years old and loved performing in musicals at high school. At 17, she went to a special school for the arts but later left because she wanted to become a professional singer as soon as possible. She became a global star with her first album The Fame in 2008 and followed it in 2009 with The Fame Monster. Earlier this year she released  a single, "Born this Way," which broke the record for quickest sales for a piece of music on iTunes, with one million downloads in only five days. Her third album, also called Born this Way, went on sale in May this year. www.ks5u.com Because of how much money she earns, how much she is written and talked about in the media, and how many internet searches are made with her name, Forbes magazine recently put her at number one in its list of the "world's most powerful celebrities ." Most music critics  say that what makes Lady Gaga's music stand out are her strong voice and also the strong electronic rhythm of most of her songs, which makes them popular in nightclubs. They also say her music often sounds like the work of other artists, and she herself is quite open about the fact that groups such as Queen and female singers such as Madonna have been a big influence on her. More original than her music, perhaps, is the way she looks. A big part of her image is her outlandish  clothes, with her strangest piece of clothing probably having been a dress made partly out of meat, which she wore once in 2010. Part of what has made Lady Gaga so famous so quickly is the way she has used social media. She has over 30 million Facebook friends, for example, and almost 10 million followers on Twitter. What can we learn about "iTunes"?  It is   _  .
a single album of popular songs on sale. a mobile phone which shows live music performances. a center where pop stars get together. a software used to download music from the Internet.