With no explanation, label each line with "O", "art-broadcastprogram", "art-film", "art-music", "art-other", "art-painting", "art-writtenart", "building-airport", "building-hospital" or "building-hotel" preceded by ":".
When
a
siege
tower
was
near
a
wall
,
it
would
drop
a
gangplank
between
it
and
the
wall
.
When:O
a:O
siege:O
tower:O
was:O
near:O
a:O
wall:O
,:O
it:O
would:O
drop:O
a:O
gangplank:O
between:O
it:O
and:O
the:O
wall:O
.:O