Test
tubes
laid
on
the
bench
may
____________________
off
the
edge
and
____________________
to
the
ground
.
Do
not
return
the
solution
in
the
test
tube
to
the
reagent
bottle
to
avoid
____________________
.
Never
hold
the
dropper
____________________
____________________
.
Otherwise
,
the
solution
will
go
into
the
rubber
bulb
.