['they', 'do', 'it', 'EmptyParameter', 'EmptyParameter'] ['they', 'reach', 'planet', 'EmptyParameter', 'EmptyParameter'] ['they', 'head', 'EmptyParameter', 'EmptyParameter', 'EmptyParameter']
['<PRP>', 'act-114', '<PRP>', 'EmptyParameter', 'EmptyParameter'] ['<PRP>', 'get-13.5.1', "Synset('natural_object.n.01')", 'EmptyParameter', 'EmptyParameter'] ['<PRP>', 'conduct-111.1', 'EmptyParameter', 'EmptyParameter', 'EmptyParameter']
They can't do it until they have reached the planet they are heading for.
<PRP> can't do <PRP> until <PRP> have reached the Synset('natural_object.n.01') <PRP> are heading for.