Graffiti（涂鸦） Street art is a very popular form of art that is spreading quickly(quick) all over the world．You can find it on buildings, sidewalks, street signs and dustbins in many big （41）_____(city) of the world．Street art has gained great（42）_____(popular). Even art museums and galleries are（43）_____(collect) the works of street artists. Street art started out very（44）_____(secret) because it is illegal to paint public and private property without permission. People often have different（45）_____(opinion) about street art. Some think it is a crime and others think it is a very（46）_____(beauty) new form of culture.Art experts claim that the（47）_____(move) began in New York City in the 1960s. Young adults（48）_____(spray) words and other images on walls and trains. This（49）_____(color), energetic style of writing became（50）_____(know) as graffiti._____