How do people traditionally manufacture   things? They usually start with a sheet of metal, wood or other material and cut, drill   and shave it to create a desired shape. Sometimes, they use a mold   made of metal or sand, pour liquid plastic or metal into it and let it cool to create a solid part. Now, a completely different method is gaining popularity. On Oct. 9, 2013, London Science Museum kicked off its new exhibition, 3-D: Printing the Future, with over 600 3-D printed objects on display, including space probes  , toy dolls and even human organs - basically any product you can think of, reported Live Science. You might find it hard to believe that an object can actually be "printed out" like a picture. But it is not that hard to understand how it works. Just as a traditional printer sprays   ink onto paper line by line, modern 3-D printers spread material onto a surface layer by layer, from the bottom to the top, gradually building up a shape. Instead of ink, the materials the 3-D printer uses are mainly plastic, resin   and certain metals. The thinner each layer is - from a millimeter to less than the width of a hair - the smoother and finer the object will be. And objects always come out in one piece, sparing you the trouble of putting different parts together afterward. For example, 10 years ago a desktop 3-D printer might have cost PS20,000 (200,000 yuan), while now it costs only about PS1,000, according to the BBC. In fact, 3-D printers have been around for some time, but until recently they hadn't been very popular since few people could afford them. Last year, though, saw a big decrease in the price of 3-D printers. However, as 3-D printing technology becomes more commonplace, it may trigger certain problems. One of them is piracy  . "Once you can download a coffee maker, or print out a new set of kitchen utensils   on your personal 3-D printer, who will visit a retail   store again?" an expert on 3-D printing told Forbes News. Even more frightening, the world's first 3-D printed gun was successfully fired in the US in May of this year, which means that 3-D printing could potentially give more people access to weapons. What was the big event that happened in the 3-D printing industry last year?
Over 600 3-D printed objects were on display in an exhibition. 3-D printing technology came to be used in various fields. The world's first 3-D printed gun was successfully made. The 3-D printer became more affordable for consumers.
Question: How do people traditionally manufacture   things? They usually start with a sheet of metal, wood or other material and cut, drill   and shave it to create a desired shape. Sometimes, they use a mold   made of metal or sand, pour liquid plastic or metal into it and let it cool to create a solid part. Now, a completely different method is gaining popularity. On Oct. 9, 2013, London Science Museum kicked off its new exhibition, 3-D: Printing the Future, with over 600 3-D printed objects on display, including space probes  , toy dolls and even human organs - basically any product you can think of, reported Live Science. You might find it hard to believe that an object can actually be "printed out" like a picture. But it is not that hard to understand how it works. Just as a traditional printer sprays   ink onto paper line by line, modern 3-D printers spread material onto a surface layer by layer, from the bottom to the top, gradually building up a shape. Instead of ink, the materials the 3-D printer uses are mainly plastic, resin   and certain metals. The thinner each layer is - from a millimeter to less than the width of a hair - the smoother and finer the object will be. And objects always come out in one piece, sparing you the trouble of putting different parts together afterward. For example, 10 years ago a desktop 3-D printer might have cost PS20,000 (200,000 yuan), while now it costs only about PS1,000, according to the BBC. In fact, 3-D printers have been around for some time, but until recently they hadn't been very popular since few people could afford them. Last year, though, saw a big decrease in the price of 3-D printers. However, as 3-D printing technology becomes more commonplace, it may trigger certain problems. One of them is piracy  . "Once you can download a coffee maker, or print out a new set of kitchen utensils   on your personal 3-D printer, who will visit a retail   store again?" an expert on 3-D printing told Forbes News. Even more frightening, the world's first 3-D printed gun was successfully fired in the US in May of this year, which means that 3-D printing could potentially give more people access to weapons. What was the big event that happened in the 3-D printing industry last year?
A. Over 600 3-D printed objects were on display in an exhibition.
B. 3-D printing technology came to be used in various fields.
C. The world's first 3-D printed gun was successfully made.
D. The 3-D printer became more affordable for consumers.
Answer: