Two or more characters conversing is a dialogue (B).
It is either a written or spoken exchange between two or more people. The term comes from the greek <em>dialogos</em>. Its roots are "<em>dia</em>: through and <em>logos</em>: speech; reason. The first author who used this was Plato in whose works it is closely associated with the art of dialectic.
If it takes 3 days to mail in, and if you want to mail it in on Monday, you have to mail it in on Friday, and then the payment will be received on Monday.