How do I select best answer on yahoo answers itself?

Say Ive just asked a question and someones answered it that I think deserves best answer, how do I do it, because on all of my answers I cannot do it... Can you not do it?

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).