Please remain seated until the plane_____to complete landing.
You can only be sure of_________ you have at present; you cannot be sure of something _____ you might get in the future.
Could I speak to__________ is in charge of International Sales ,please?
The traditional view is ______ we sleep because our brain is “programmed” to make us do so.
______ he referred to in his article was unknown to the general reader.
____ matters most in learning English is enough practice.