How does sudo remember you already entered root's password?

My Yahoo password has been changed and I can't remember the date of birth I entered?

• I am writing this on behalf of my friend as Yahoo wont let him retrieve his password without his date of birth and now he can't access his account and all his important data, he had an alternate email when he created it, but there is no option of it being sent there!

• Answer:

  Oh dear, Your friend may have to open a different account the birthday you enter has to be true along with country or state postal zip code the Secret question These are used to help in the event either you or your friend forget the password or user name. Help your friend with this let your friend know how important it is to keep things up to date. although the birthday doesn't change.