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 ":".
At
its
most
active
during
the
1940s
,
the
mine
produced
2,500
tons
of
micaceous
haematite
per
year
.
At:O
its:O
most:O
active:O
during:O
the:O
1940s:O
,:O
the:O
mine:O
produced:O
2,500:O
tons:O
of:O
micaceous:O
haematite:O
per:O
year:O
.:O