AIR ________ IS ONE OF THE MOST SERIOUS PROBLEMS THAT MANYCOUNTRIES...
6. Air ________ is one of the most serious problems that many
countries in the world have to face nowadays.
A. sewage
B. fume
C. pollution
D. smoke
6. Air ________ is one of the most serious problems that many
countries in the world have to face nowadays.
A. sewage
B. fume
C. pollution
D. smoke