Question
Why is it important for a seed to stay dormant for a long time?

Answer
Hi Abdulla,
Thanx for your question.  Normally, I don't do homework questions because I think it is important for you to do your own reserch rather than ask someone for a quick answer.  This is a botanical question however, I have spent a lot of time studying dormancy in seeds.  So, here goes.  Basically, nature has established a dormancy requirement in some seeds to protect the seed from germinating at the wrong time.  Seeds that have a dormancy requirement have that requirement to prevent them from arbitrarily germinating in the winter when the cold would kill the seedling.  Mostly it is plants plants that grow where there are cold winters that have this dormancy requirement.  Here is a link you might find helpful.

http://www.ces.ncsu.edu/depts/hort/hil/hil-8704.html

I hope this helps.
Tom