Given the task definition and input, reply with output. This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.

Passage: For decades after the Second World War, any national symbol or expression was a taboo. However, the Germans are becoming increasingly patriotic. During a study in 2009, in which some 2,000 German citizens age 14 and upwards filled out a questionnaire, nearly 60% of those surveyed agreed with the sentiment "I'm proud to be German." And 78%, if free to choose their nation, would opt for German nationality with "near or absolute certainty". Another study in 2009, carried out by the Identity Foundation in Dusseldorf, showed that 73% of the Germans were proud of their country, twice more than 8 years earlier. According to Eugen Buss, a sociology professor at the University of Hohenheim, there's an ongoing normalisation and more and more Germans are becoming openly proud of their country.
What war was followed by an increase in national symbols?