For years scientists have been worried about ________of air pollution on th eearth’s natural conditions.
举一反三
- This performance has been achieved in the most toughest market conditions we have seen for many years yet.( )
- Softening Claims” Using natural gas instead of coal ______ prevent air pollution”
- I __________Tom for about ten years now. A: have been knowing B: have known C: knew
- People’s life standards, health conditions and education have been improved by the revolution of ______.
- Because air pollution has been greatly reduced, this city is still _______ .