Please answer the following question: Read the article and select the best answer. Article: Zipped into a bag, it looks like a large umbrella. Unfolded, it goes along the street like any other bicycle. It's the "A-bike", the brainchild of British inventor Sir Clive Sinclair, who made history in the 1970s by developing the world's first pocket calculator. He described his new invention as "the world's smallest, lightest foldable bicycle". "My original thought was that if you could have a bicycle that was dramatically lighter and more firm than the ones that exist today, it would change the way in which bicycles are used,"said Sinclair. The mini-bike, showed in Singapore last week and set to go on sale worldwide in 2005 at a price of nearly US$300, is built for riders as heavy as 112 kilograms and is height-adjustable . It takes about 20 seconds to fold or unfold. Its wheels are a quarter the size of those on a regular bicycle, but Sinclair promises a smooth ride for most cyclists. "You require no extra energy to ride the A-bike and it can go up to 15 miles per hour (24 kilometers per hour)," he said. Constructed mainly of plastic, the 5.5-kilogram bicycle folds into a package of less than 0.03 cubic meters . Sinclair also invented the first pocket TV in 1984 and the futuristic C5 electric tricycle in 1985. He said he hoped the bicycle would attract common citizens, officials, campers or anyone needing transport for a short trip and he said the next step for the A-bike was to add an electric motor in a few years. Question: The most important character of this kind of bike is its _ . Options: A: big size B: light weight C: beautiful appearance D: foldable structure
Answer:
D