With no explanation, label each line with "location-GPE", "O", "art-broadcastprogram", "art-film", "art-music", "art-other", "art-painting", "art-writtenart", "building-airport" or "building-hospital" preceded by ":".
It
remains
the
worst
school
related
mass
murder
in
U.S
.
history
.
It:O
remains:O
the:O
worst:O
school:O
related:O
mass:O
murder:O
in:O
U.S:location-GPE
.:location-GPE
history:O
.:O