The best way to explore _______ countryside is on _______foot.
________ many times, he finally understood it.
He told us whether _________ a picnic was still under discussion
David threatened_______ his neighbour to the police if the damages were not paid.
Ladies and gentlemen, please remain __________ until the plane has come to a complete stop.
Bill suggested _____ a meeting on what to do for the Shanghai Expo during the vacation.