A．It was difficult to print.
B．It was hard to come by.
C．It was hard and breakable.
D．It was extremely expensive.
A．It is the latest model of a 3D printer.
B．It is a plastic widely used in 3D printing.
C．It gives fashion designers room for imagination.
D．It marks a breakthrough in printing material.
A．They arise from the advances in technology.
B．They have not been examined in detail so far.
C．They are easy to solve with modern technology.
D．They can’t be solved without government support.