27678
Clearly , catalyst choice , in particular topology and acidity , as well as the specific process conditions determine the overall MTO activity and selectivity ; however , the subtle balances between these factors remain not fully understood .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities:  
Answer:
 None