As for this problem together with the options as answers presented with it, the most probable and the most likely answer would be C. the purpose of the communication.
The first thing you must consider in any type of communication is the purpose of the communication itself. Determining the purpose behind the communication would, in turn, pave way to determining the other things that is needed to be determined such as the type of communication, the style of communication, the timing of the communication, and so on and so forth.