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. 

A, c, and d are the answers