It was in 1969 ______ two Americans went to the moon by spaceship.
Its hard to ________ the green beans from the red ones, because there are too many of them.
Never before _______ seen anybody who can play tennis as well as Robert.
______ her roommates, the girl stepped into the room quietly.
_________ environmental damage is done, it takes many years for the ecosystem to recover.
----Where did you get to know her? ----It was on the farm ________ we worked.