The best way to explore _______ countryside is on _______foot.
There are some health problems that, when ______ in time, can become bigger ones later on.
He commanded that all the gates ________.
As is known to us all, English books of this kind ________ well in middle schools.
_______ everyone here, I wish you a pleasant journey back to your country.
I think you need some outdoor exercise. Plenty of fresh air will ________good health.