You can only be sure of _____ you have at present; you cannot be sure of something _____ you might get in the future.
In doing scientific experiments one must be _______ careful with the instruments.
She _______ to the waiter whose language isn’t ______ hers to bring some more coffee.
As to the subject, we have consulted the most _______ professor who gave us _______ explanation.
“ Do you mind if I keep pets in this building?” “________________”
The headmaster could not go to the meeting; therefore, Mr. Smith _______ him.