Experiments of this kind __________ in both the U. S. and Europe well before the Second World War started.
We heard an explosion and________for cover.
China is one of the largest countries in the world,________9.6 million square kilometres.
Robert is said________abroad, but I don't know what country he studied in.
________down the radio—the baby's asleep in the next room.
He was suddenly________with a strange illness when he was about to finish the work.