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 ":".
By
the
1920s
,
that
proportion
had
risen
to
20
percent
.
By:O
the:O
1920s:O
,:O
that:O
proportion:O
had:O
risen:O
to:O
20:O
percent:O
.:O