Considering his health, I advise him to ______ an hour or two each day to work out.
_____ when one loses freedom does one know its value.
Little Jim is going to spend his holiday in Paris, _____ lives his uncle.
The problem is not _____ easy. Think _____ over.
It is so difficult a problem that _____ student in this class _____ work it out.
Mr Zhang gave all the textbooks to all the pupils , except _____ who had already taken them .