28. The purpose of the passage is to .

A. attract consumers to buy 3D printers

B. explain the importance of 3D printing

C. introduce a new technique—3D printing

D. describe the rapid development of technology

29. The Build Shop LLC is a store .

A. selling sewing machines

B. known for tools like 3D printers

C. promoting 3D printers

D. offering 3D printing classes and services

30. In the UPS Store, the cost of printing a 3D object depends on .

A. the amount of materials

B. the labor services it needs

C. the materials and labor services

D. the size of the object

31. The attitude of KiChong Tran towards the development of 3D printing is .

A. objective B. positive C. uncertain D. critical