With no explanation, label each line with "location-GPE", "O", "art-broadcastprogram", "art-film", "art-music", "art-other", "art-painting", "art-writtenart", "building-airport" or "building-hospital" preceded by ":".
They
descend
through
the
Pennsylvania
and
Maryland
Piedmont
,
before
reaching
sea
level
at
Elkton
,
the
head
of
navigation
.
They:O
descend:O
through:O
the:O
Pennsylvania:location-GPE
and:O
Maryland:location-GPE
Piedmont:location-GPE
,:O
before:O
reaching:O
sea:O
level:O
at:O
Elkton:location-GPE
,:O
the:O
head:O
of:O
navigation:O
.:O