Without your writing would only be a list of main ideas. A. details
B. distracters
C. a purpose
D. an audience

I believe it can be A details or C Purpose

Its A i had did the test and got it right

The most important characteristic is determining your audience. 

In order to have the correct tone, you must know your audience. Is your audience a wealthy businessman? Then you need an intellectual, logical, and formal tone. Is the audience a friend? Then an informal tone is fine.