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In the 10th century , Emperor Alexander ( r. 912 – 913 ) introduced a bust of Christ on the obverse , and Romanos I ( r. 920 – 944 ) added an imperial bust to the center of the cross .
 person: Alexander; person: Romanos I
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities: Alexander, Romanos I 
Answer:
 person: Alexander; person: Romanos I