You don't. You ring them and say you had an interview with B (plus date, location etc.). Say you understand that it takes time to reach the right decision but t

You don't. You ring them and say you had an interview with B (plus date, location etc.). Say you understand that it takes time to reach the right decision but that you wonder if there is anything you can contribute or expand upon that would help them make up their mind in your case. Cant hurt and might tip the balance.