7429
Extrusion-based printing frequently requires a hollowing step to remove material from inside of artifacts and subsequently reduce the amount of material , printing time , product weight , energy consumption , and ultimately , the cost .
 step, material, material, weight
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:
 step, material, material, weight