['density', 'increase', 'EmptyParameter', 'year', 'over']
["Synset('placement.n.01')", 'other_cos-45.4', 'EmptyParameter', '<DURATION>4', 'over']
The density of the water has been increasing over the past few years.
<DURATION>4 Synset('placement.n.01') of <DURATION>4 Synset('physical_entity.n.01') has been increasing over <DURATION>4.