A 3D printer cannot make any object on demand like the Star Trek replicators of
science fiction. But a growing array of 3D printing machines have already begun        【D1】________
to revolutionize the business of making things in the real world. 3D printers
work by follow a computer's digital instructions."print" an object using                        【D2】________
materials such as plastic, ceramics and metal. The printing process involve                   【D3】________
building up an object one layer at a time until its complete. For instance,                     【D4】________
some 3D printers squirt out a stream of heated, semi-liquid plastic that
solidifies as printer's head moves around to create the oudine of each                         【D5】________
layer within the object The instructions use by 3D printers often take the form            【D6】________
of computer-aided design (CAD) files digital blueprints for making different                【D7】________
objects. That means a person can be design an object on their computer using           【D8】________
3D modeling software, hook the computer up to a 3D printer, and then watch
the 3D printer build the object right in their eyes. Most 3D printers                              【D9】________
don't go beyond the size of household appliances such as refrigerator, but
3D printing could even scale up in size build objects as big as a house.                       【D10】________

【D1】

【D2】

【D3】

【D4】

【D5】

【D6】

【D7】

【D8】

【D9】

【D10】