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Various material systems have been created for 3D printing of sand molds ; however , a formal study of the materials ’ effects on cast products has not yet been conducted .
 Various material, 3D printing, sand, molds, materials, cast
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:
 Various material, 3D printing, sand, molds, materials, cast