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 thegovernment,in schools or in business.
Soon, computers will be found in every home,too. Wehave good reason to say that computers are playing an increasingly important role in our life and we have stepped intothe Computer Age.