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 ":".
The
Mexican
forces
fell
back
from
Chapultepec
and
retreated
within
the
city
.
The:O
Mexican:location-GPE
forces:O
fell:O
back:O
from:O
Chapultepec:location-GPE
and:O
retreated:O
within:O
the:O
city:O
.:O