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In lab sessions , students operate and characterize desktop AM machines , and work in teams to design and fabricate a bridge having maximum strength per unit weight while conforming to geometric constraints .
 AM machines, design, fabricate, bridge, strength, 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:
 AM machines, design, fabricate, bridge, strength, weight