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They can be divided into four types : a transition between two materials , three materials or above , switched composition between different locations or a combination of density and compositional gradation .
 material: be; concept or principle: transition; concept or principle: materials; concept or principle: materials; concept or principle: composition; machanical property: density
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:
 material: be; concept or principle: transition; concept or principle: materials; concept or principle: materials; concept or principle: composition; machanical property: density