1903
The dilemma may be caused by two factors : the TO researcher has a lack of knowledge on the AM processes or the direct embedding of AM constraints with mathematical models in the 2D or 3D TO processes is quite tough .
 material: be; manufacturing process: AM processes; manufacturing process: AM; concept or principle: mathematical; concept or principle: 2D; concept or principle: 3D; concept or principle: processes
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; manufacturing process: AM processes; manufacturing process: AM; concept or principle: mathematical; concept or principle: 2D; concept or principle: 3D; concept or principle: processes