Gmail help needed, how do I get rid or sent emails read below please ?

When I create an email, in choosing whom to send to I can like hold down "a" and get a list of everyone I've communicated with whose email addy begins with "a". How do I get rid of these, I didn't add them it must do it by themselves. I'd like to get rid of the old business ones.
Gmail help needed, how do I get rid or sent emails read below please ?
on the left side, either click contacts or show all (under your list of quick contacts) Then delete the addresses you don't want anymore.
Reply:Gmail adds them to your Contact list, i don't know how to stop it from doing this, but if you want to delete some of them just click on the 'Contacts' link on the left hand side of the page, select unwanted contacts and press the delete them.