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 ":".
They
conducted
a
study
of
specimens
collected
in
a
7-week
period
(
December
2001
–
February
2002
)
in
851
infants
and
children
.
They:O
conducted:O
a:O
study:O
of:O
specimens:O
collected:O
in:O
a:O
7-week:O
period:O
(:O
December:O
2001:O
–:O
February:O
2002:O
):O
in:O
851:O
infants:O
and:O
children:O
.:O