A virus is a microscopic organism that can replicate only inside the cells of a host organism. Most viruses are so tiny they are only observable with at least a conventional optical microscope.
Recognized by the Guiness Book of World Records as the MMO with the longest play time per player, and easily the oldest game on this list (launching four years ahead of World of Warcraft, way back in 2001), Runescape deserves mention because it's one of the most updated and popular games of any kind on the planet.
The metro network is planned to be expanded up to a length of 877km with 22 lines. The annual ridership of the metro in 2012 was 2.276 billion. Beijing Subway, China. Beijing Subway, Chinaâs oldest metro system, currently ranks as the worldâs third longest subway system comprising of 17 operatinglines spanning a total length of 456km.