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
front
sight
is
contained
in
a
protective
cage
with
a
hole
in
the
top
to
insert
an
elevation
adjustment
tool
,
while
the
rear
sight
is
shielded
by
two
metal
ears
.
The:O
front:O
sight:O
is:O
contained:O
in:O
a:O
protective:O
cage:O
with:O
a:O
hole:O
in:O
the:O
top:O
to:O
insert:O
an:O
elevation:O
adjustment:O
tool:O
,:O
while:O
the:O
rear:O
sight:O
is:O
shielded:O
by:O
two:O
metal:O
ears:O
.:O