1987
All down-facing surfaces have typically rougher surfaces than upwardB-facing surfaces , thin angled features suffer from stair-step effects , and small angles require supports .
 concept or principle: surfaces; concept or principle: surfaces; concept or principle: surfaces; application: supports
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: 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:
 concept or principle: surfaces; concept or principle: surfaces; concept or principle: surfaces; application: supports