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Conversely , when 2000 grit sandpaper is used to mechanically prepare the surfaces , the resulting films have poor electrical conductivity and optical reflectance , but excellent adhesion .
 sandpaper, surfaces, electrical conductivity, optical, adhesion
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:
 sandpaper, surfaces, electrical conductivity, optical, adhesion