---He has been working hard all the time.---__________ he got full marks in the last English test.
The research is so designed that once _______ nothing can be done to change it.
Having a trip abroad is certainly good for the old couple, but it remains _______ whether they will enjoy it.
_______ such heavy pollution already, it may now be too late to clean up the river.
Robert is said _______ abroad, but I don’t know what country he studied in.
The purpose of new technologies is to make life easier, _______ it more difficult.