D

The U．K．based company，Gumdrop Ltd，has come up with a brilliant idea that enables easy disposal(处理)of chewed gum using specializedrecycling bins．Passersby cansimply put any unwanted chewing gum into the bright pink receptacles(容器)that have been installed    across the city of London．Once full，they are mailed to Gumdropheadquarters where the gum is recycled to other useful things like rubber bootsand phone cases as well．  

Though thepink bins clearly indicate that they are meant for gum recycling，there is always the risk that peoplewill use them to get rid of all kinds of waste．To ensure that it is just gum that gets recycled，the company has developed a specialsystem that extracts(提取)any foreign items that have been mixed in．   

Anna Bullus，who founded the company in 2009，says she was inspired to create theclever receptacles after observing the sticky mess caused by gum waste on thestreets of London ．To test if people would be willing to dispose of gum responsibly，she set up two bins inside a men’s restroom at Southampton Airport．It was extremely successful! Bullussays they had to pick up the full receptacles five times a year，which cost the company$300 USD．

While thetest convinced Bullus that she was on the right track，it took another three years beforethe pink receptacles were adopted by Legoland outside of London．Their success has led to the rapiddeployment of the bright pink bins in the country’s streets，offices and even schools．

Bullus nowhopes to take her Gumdrops to countries around the world．Among the top on her list is the U．S．A where an estimated 59％of the population chews gum! The company has also introduced GumdropOn-the-Go—a personalrecycling device that can be attached to key chains enables consumers to getrid of gum waste in a responsible manner．

33．By what test did Bullus know her idea was practical?