the poster is a persuasion because it talks about undermining war effort, which you would not want to do, so its is persuading you to do you part in silence. that means not giving info away
stairs : ) i believe is your answer
the correct answer is a. how to make proposal that works.
indeed, the register is quite formal and the tone is especially objective as it avoids the use of the first and second person singular (i, you) and opts instead for the third person plural which is more impersonal and focuses on the data and the argument that is being developed by the author. the formality adds the impression of respectability to the work and the impersonality adds objectivity to it.