31. There's has been a steady rise in the average temperature around the planet over the last hundred years or so, and the majority of scientists put it ____ to human activity.
A. down B. back C. up D. across
32. However, some scientists argue that the historical evidence shows that over time the Earth heats __ and cools _ naturally.
A. up - away B. away - down C. up-down D. down - up
33. It is predicted that over the next few decades many species will die ____ as once fertile areas turn to desert.
A. off B. out С. up D. down
34. Most of the air pollution results ____ the burning of fossil fuels, motor vehicles, factories, aircraft and rockets.
A. in B. to C. on D. from
35. Environmental pollution is becoming an ____ serious problem that needs to be taken care of as soon as possible.
A. increasingly B. increasing C. increase D. increased
