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表示重要、必要、困难、方便、可能
1)It is important(necessary，difficult，convenient， possible)for sb.to do sth.
2)We think it necessary to do sth.
3)It plays an important role in our life.
例如：
Computers are now being used everywhere， whether in the government，in schools or in business.Soon， computers will be found in every home，too. We have good reason to say that computers are playing an increasingly important role in our life and we have stepped into the Computer Age.
