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 ":".
The
tunnelling
units
were
occupied
in
offensive
and
defensive
mining
involving
the
placing
and
maintaining
of
mines
under
enemy
lines
,
as
well
as
other
underground
work
such
as
the
construction
of
deep
dugouts
for
troop
accommodation
,
the
digging
of
subways
,
saps
(
a
narrow
trench
dug
to
approach
enemy
trenches
)
,
cable
trenches
and
underground
chambers
for
signals
and
medical
services
.
The:O
tunnelling:O
units:O
were:O
occupied:O
in:O
offensive:O
and:O
defensive:O
mining:O
involving:O
the:O
placing:O
and:O
maintaining:O
of:O
mines:O
under:O
enemy:O
lines:O
,:O
as:O
well:O
as:O
other:O
underground:O
work:O
such:O
as:O
the:O
construction:O
of:O
deep:O
dugouts:O
for:O
troop:O
accommodation:O
,:O
the:O
digging:O
of:O
subways:O
,:O
saps:O
(:O
a:O
narrow:O
trench:O
dug:O
to:O
approach:O
enemy:O
trenches:O
):O
,:O
cable:O
trenches:O
and:O
underground:O
chambers:O
for:O
signals:O
and:O
medical:O
services:O
.:O