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
the
height
of
construction
activity
,
the
workforce
is
believed
to
have
involved
upwards
of
2,700
men
.
At:O
the:O
height:O
of:O
construction:O
activity:O
,:O
the:O
workforce:O
is:O
believed:O
to:O
have:O
involved:O
upwards:O
of:O
2,700:O
men:O
.:O