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Tensile test specimens were designed and printed in three types : ( A ) a single-material specimen printed by a single extrusion head ; ( B ) a single-material but multi-section specimen printed in a zebra-crossing structure by two extrusion heads ; and ( C ) a multi-material specimen printed with two materials in a zebra-crossing pattern .
 Tensile test, designed, extrusion head, B, structure, extrusion heads, C, multi-material, materials, pattern
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:
 Tensile test, designed, extrusion head, B, structure, extrusion heads, C, multi-material, materials, pattern