The answer would be all of the above. You should consider what your audience already might know so that you don't repeat the things that they do. You need to know where you can find credible sources of information to support your thesis statement. You definitely need to know what the purpose of your report is, because if you are writing without a purpose, your report will sound unprofessional and badly written. So, the correct answer would be:
C) All of the above
Hope this answer helped!