The best way to explore _______ countryside is on _______foot.
His _____ English is very good, because he is from Australia, an _____ country.
He always takes full _____ of the mistakes made by his rivals(对手) to win the election.
Some researchers believe that there is no doubt _____ a cure for AIDS will be found.
Use the umbrella to ______ yourself from the rain.
____ for a long time, but he managed to catch up with his classmates at last.