THE teenage boy is becoming a man. Justin Bieber released his single, Boyfriend, on March 26. With it the 18-year-old crossed the bridge between adolescence (青春期) and adulthood, and landed on his feet with a smile. Bieber sounds all grown up in this single since Never Say Never in 2011. Billboard magazine said the song sees Bieber stepping into the shoes vacated (让出) by Justin Timberlake, who is now pursuing an acting career.