All of the following must exist for there to be demand except a. a necessity to buy a product. c. an ability to buy a product. b. producers to sell a product. d. a willingness to buy a product.

The answer is ethnic groups.

Economic success prussia had a very strong economy, partly due to the success of the zollverein. stronger prussian army king wilhelm wanted to build a bigger, stronger army but was blocked by the prussian landtag (parliament).-credits to google for putting answer -credits to slideshare for making answer-credits to me for putting answer on brain.ly