Detailed Instructions: Given a sentence and two mentions from the text (arguments), indicate a phrase (a verb or noun phrase) that describes the relationship between the provided arguments.
Q: Sentence: 'When David Stern started his tenure as the NBA 's commissioner 25 years ago , none of the aforementioned men had been born yet .', Argument/Subject 1: 'david stern', Argument/Subject 2: 'nba'
A:
be commissioner of