With no explanation, label each line with "O", "event-attack/battle/war/militaryconflict", "art-broadcastprogram", "art-film", "art-music", "art-other", "art-painting", "art-writtenart", "building-airport" or "building-hospital" preceded by ":".
They
had
three
sons
,
the
two
elder
of
whom
were
killed
in
the
First
World
War
:
They:O
had:O
three:O
sons:O
,:O
the:O
two:O
elder:O
of:O
whom:O
were:O
killed:O
in:O
the:O
First:event-attack/battle/war/militaryconflict
World:event-attack/battle/war/militaryconflict
War:event-attack/battle/war/militaryconflict
::O