I can’t believe that there are _____ many poor people in ____ a rich country.
We have to ______ a time to discuss the matter again.
Ever since my brother graduated from the university, he _______ in the present company for 15 years and he is now chief engineer of the company .
The athlete fell off his bike when he _____ down the hill.
You can’t be ______ when you camp _____ an high altitude, where the air is thin.
I’d prefer ______ in the office rather than _____ at home watching TV.