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.

[EX Q]: Given Relationship: 'land on', Sentence: 'Phoenix - Mission to land on Mars .'
[EX A]: land

[EX Q]: Given Relationship: 'be professor of', Sentence: 'Your nerves learn to communicate more effectively with your muscle cells , allowing the muscle to recruit more cells during each contraction , says Mark A. W. Andrews , PhD , associate professor of physiology at Lake Erie College of Osteopathic Medicine in Erie , Pa .'
[EX A]: professor

[EX Q]: Given Relationship: 'be president of', Sentence: 'Times are a changing in the United States today as president George Bush leaves the Oval Office for the final time - to be replaced by Democratic president-elect Barack Obama .'
[EX A]:
president