What was the most prevalent propaganda media form?

if World War One, posters were prevalent in Britain and Germany because they could target at any audience

but in Britain it targeted the ordinary citizen, in Germany it targeted the intellectual

propaganda was a way of providing the idealist projection of a certain view for example the government. it often lied to get a point across.

NOT billboards

Explanation:

Got it wrong on the test

the term is einsatzgruppen