1.I only see my grandparents once in a blue ______.moonskynightday2.Keep in

1.I only see my grandparents once in a blue ______.
moon
sky
night
day
2.Keep in _____ that most software soon goes out of date.
head
хэнд
eye
mind
3. She has been walking in the park ____ 5 hours already, so something was going on.
for
around
even
since
4. Continue your experiment, never give ____ and success will appear unexpectedly.
off
of
up
in