Given the task definition and input, reply with output. From the given sentence, extract the phrase (often noun or verb) that carries the given relationship. The generated phrase should be present in the sentence.

Given Relationship: 'be head of', Sentence: 'On 15 November Mohamed ElBaradei , head of the International Atomic Energy Agency , the UN 's nuclear weapons "watchdog , " acknowledged that he really does n't know the state of Iran 's nuclear weapons program .'
head