I would definitely say B.) A smile because if you were just staring it may be rude or distracting to the speaker and a smile shows you are listening and absorbing the knowledge
It takes 20 years to build a reputation and five minutes to ruin it. If you think about that, you'll do things differently.” Here, Buffett says that anyone's reputation can quickly take a hit and to always act with integrity. Otherwise, a whole career can be ruined easily no matter the effort over the years.
