We heard an explosion and________for cover.
The science of computer, _______rapid progress has been made in recent years, is the most important of all science.
-----Can you come for dinner on Sunday or Saturday? -----I’m afraid _______ day is possible.
It is not just the size of the Olympic Games ___makes them unique, but ____they mean to us .
-----Now, where is my ticket ? -----______. We will be late for the film.
The astronauts started their journeys in rockets _____ forward by jets of hot gas.