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
are
usually
surrounded
by
moats
,
unless
they
are
constructed
on
hills
.
They:O
are:O
usually:O
surrounded:O
by:O
moats:O
,:O
unless:O
they:O
are:O
constructed:O
on:O
hills:O
.:O