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 ":".
When
Alaska
was
purchased
by
the
United
States
in
1867
,
slavery
became
illegal
in
Alaska
.
When:O
Alaska:location-GPE
was:O
purchased:O
by:O
the:O
United:location-GPE
States:location-GPE
in:O
1867:O
,:O
slavery:O
became:O
illegal:O
in:O
Alaska:location-GPE
.:O