With no explanation, label each line with "product-other", "product-airplane", "O", "art-broadcastprogram", "art-film", "art-music", "art-other", "art-painting", "art-writtenart" or "building-airport" preceded by ":".
The
helicopters
saw
a
radio
antenna
and
were
fired
on
and
at
16:30
aero-rifle
troops
were
landed
nearby
,
but
were
quickly
pinned
down
by
enemy
fire
.
The:O
helicopters:product-airplane
saw:O
a:O
radio:product-other
antenna:product-other
and:O
were:O
fired:O
on:O
and:O
at:O
16:30:O
aero-rifle:product-other
troops:O
were:O
landed:O
nearby:O
,:O
but:O
were:O
quickly:O
pinned:O
down:O
by:O
enemy:O
fire:O
.:O