You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.
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Question: Category: HISTORIC BOOKS 
Clue: It was written in 1924 in the fortress of Landsberg am Lech

Answer: mein kampf by adolf hitler


Question: Category: FINANCE HISTORY 
Clue: In the 19th c., selling stock you didn't yet own, hoping it would fall, was called selling this animal's skin

Answer: a bear


Question: Category: TECHNOLOGY 
Clue: In 1933 Marconi set up one of the first microwave radio systems, between Castel Gandolfo & this sovereign state

Answer:
vatican city