2031
A computerized database of veterans discharged from the military after 1967 was selected as the source because it contains about 50 % of the total Vietnam era veteran population , is reasonably unbiased , and provides a feasible method for identifying twins .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
Answer:
 None