With no explanation, label each line with "O", "location-mountain", "art-broadcastprogram", "art-film", "art-music", "art-other", "art-painting", "art-writtenart", "building-airport" or "building-hospital" preceded by ":".
Due
to
its
steep
profile
and
unstable
weather
,
Ushba
is
considered
by
many
climbers
as
the
most
difficult
ascent
in
the
Caucasus
.
Due:O
to:O
its:O
steep:O
profile:O
and:O
unstable:O
weather:O
,:O
Ushba:location-mountain
is:O
considered:O
by:O
many:O
climbers:O
as:O
the:O
most:O
difficult:O
ascent:O
in:O
the:O
Caucasus:location-mountain
.:O