Which medium ignited what is considered a cultural revolution?
radio
television
print
film

The best answer would actually be: there were cultural revolutions following the invention of print, radio and television - each of them changed how we communicate in an abrupt and significant way, and I think that we could make a very good argument for all of them - and even for "film", but I think we can include "film" under the category of "television".

If you have to choose, I think that print is the best option: it was the first time when information was available to a large amount of people at all - before some groups of the society had a monopoly on knowledge, such as the clergy.  So print allowed to introduce more equality to the society, as more people had access to knowledge.

I think that print is the medium that led to the biggest revolution, but radio and television also inspired small revolutions on their own. 

The holy roman empire.

Ibelieve b) recall election