a
.
Air
enters
the
body
via
the
mouth
and
____________________
.
b
.
Air
travels
down
a
tube
known
as
the
____________________
.
c
.
This
tube
divides
to
form
two
____________________
taking
air
to
each
lung
.
d
.
The
bronchi
divide
further
into
smaller
tubes
called
the
____________________
.
e
.
At
the
end
of
these
smaller
tubes
there
are
air
sacs
called
the
____________________
.
f
.
These
sacs
are
covered
with
small
blood
vessels
called
____________________
.
g
.
When
the
____________________
muscle
contracts
,
the
lungs
take
in
oxygen
.
h
.
When
this
muscle
relaxes
,
air
leaves
the
____________________
.
