[tag=NN] [lemma=","] [word=they] [lemma=explore] [tag=□]
[tag=NN] [lemma=","] [word=they] [lemma=explore] [tag=DT]
[tag=NN] [lemma=","] [word=they] [lemma=explore] [tag=NN]
For instance , they explored the collisions of circular waves similar to those created by drops of water falling into a puddle .