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Owing to the lack of optimization , the dimensional accuracy of low-cost 3D printers is quite limited .
 concept or principle: optimization; process characterization: dimensional accuracy; machine or equipment: 3D printers
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
 Entities: optimization, dimensional accuracy, 3D printers 
Answer:
 concept or principle: optimization; process characterization: dimensional accuracy; machine or equipment: 3D printers