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 ":".
This
is
unusual
because
exposure
to
the
allergen
must
occur
before
the
development
of
an
allergy
.
This:O
is:O
unusual:O
because:O
exposure:O
to:O
the:O
allergen:O
must:O
occur:O
before:O
the:O
development:O
of:O
an:O
allergy:O
.:O