Answer:
Being active ( A )
Step-by-step explanation:
finding the right balance in a formal discussion is primarily about Being active during the discussion that way you will know when to listen and when you are supposed to talk/contribute towards the discussion.
Listening in a formal discussion is very vital in a formal discussion but it cannot help strike the required/right balance because a discussion is a two way factor i.e the listener should also speak during the discussion and one way one can achieve that is being actively involved in the discussion while listening attentively as well.