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In this work , a parametric study consisting of 18 experiments with unique process input combinations explores the influence of seven process inputs on the relative densities of aB-printed ( green ) alumina ( Al2O3 ) parts .
 concept or principle: process; concept or principle: process; machanical property: relative densities; material: alumina; material: Al2O3
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: process, process, relative densities, alumina, Al2O3 
Answer:
 concept or principle: process; concept or principle: process; machanical property: relative densities; material: alumina; material: Al2O3