2)It does us much harm.

　　3)It is harmfulto us.

　　例如：

　　However，everything dividesinto two.Television can also be harmful to us.It can do harm to our health and make us lazy if we spend too much time watching televi- sion.

　　4.表示重要、必要、困難、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.