PREPOSITIONS. (giới từ)
1)People are destroying the air by adding pollutants _____ it.
2)Tropical forests have supplied us _____ many sorts of plants for food, medicine, and industry.
3)We all regard pollution _____ a serious matter to human beings.
4. Our major sources of energy are now running ______.
5. It is automobiles that provide millions of people ______ transportation.