With no explanation, label each line with "O", "other-chemicalthing", "art-broadcastprogram", "art-film", "art-music", "art-other", "art-painting", "art-writtenart", "building-airport" or "building-hospital" preceded by ":".
Caesium
and
mercury
were
used
as
a
propellant
in
early
ion
engines
designed
for
spacecraft
propulsion
on
very
long
interplanetary
or
extraplanetary
missions
.
Caesium:other-chemicalthing
and:O
mercury:other-chemicalthing
were:O
used:O
as:O
a:O
propellant:O
in:O
early:O
ion:O
engines:O
designed:O
for:O
spacecraft:O
propulsion:O
on:O
very:O
long:O
interplanetary:O
or:O
extraplanetary:O
missions:O
.:O