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Three-dimensional ( 3D ) printing of functional elements during the fabrication phase of the composite structures permits the flexibility to form complex shaped reconfigurable lightweight aerospace components .
 Three-dimensional, 3D, elements, fabrication, composite structures, flexibility, lightweight, aerospace components
Please list all entity words in the text that fit the category. Output format is "word1, 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} 
Answer:
 Three-dimensional, 3D, elements, fabrication, composite structures, flexibility, lightweight, aerospace components