[填空题]The greenhouse effect causes trouble by raising the temperature of the planet. The (1) rise is not very much, but the Earth’s ecosystem is very weak, and small changes can have large effects.
It has been believed that this (2) of one degree will happen by the year 2025. This could probably (3) the North American corn belt, which produces much of the world’s grain, (4) to much higher food prices, and even less food for the Third World than they already have. However, it would also mean that some countries which are further north would be able to (5) crops they had never been able to before, although there is less land as you move north from the corn belt.
The other serious worry is that rising sea levels from the melting of the polar ice could (6) flood many countries. A rise in sea levels of one meter, which many experts are (7) by the year 2100 (and some as soon as 2030), would flood 15 percent