How do I pick a best answer if noone has answered my question?

Hi there. If your question has no answers, then you cannot choose the best answer for that question because there are no answers that could be chosen for best answer.

If your question does not receive any answers before the time that it is allowed to stay open expires, the question will be removed from Yahoo Answers, and you will get your 5 points back. To prevent this from happening in the future, if you see a question that is about to expire, go to the question and then click on the "edit" button. A drop-down menu should appear. Select the option from the drop-down menu to extend the length of time that the question stays open to give people more of a chance to answer it and so that that never happens again.

Hope this helps :P

you cannot choose a best answer if nobody answered, i think the question will be deleted when it expires and nobody answers

It will be deleted and you will get your 5 points back.