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.
One example: Sentence: 'Harry glanced again at the raw looking thing that trembled and choked in the shadow beneath the distant chair.', Argument/Subject 1: 'Harry', Argument/Subject 2: 'raw looking thing'
Solution is here: glance
Explanation: The sentence contains the generated relationship - glance, mentioned between two subjects - Harry and raw looking thing

Now, solve this: Sentence: 'Alan Greenspan , the former chairman of the Federal Reserve , told CNBC in a documentary to be shown Thursday night that he did not fully understand the scope of the subprime mortgage market until well into 2005 and could not make sense of the complex derivative products created out of mortgages .', Argument/Subject 1: 'alan greenspan', Argument/Subject 2: 'federal reserve'
Solution:
be chairman of