['they', 'begin', 'explore', 'EmptyParameter', 'EmptyParameter'] ['they', 'explore', 'X.', 'EmptyParameter', 'EmptyParameter']
['<PRP>', 'begin-55.1', 'investigate-35.4', 'EmptyParameter', 'EmptyParameter'] ['<PRP>', 'investigate-35.4', 'x.', 'EmptyParameter', 'EmptyParameter']
They begin to explore the Planet X.
<PRP> begin to explore the Synset('natural_object.n.01') X.