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: PSYCHOLOGY TERMS 
Clue: This 2-word term has its origins in a hostage-taking that followed the botched 1973 Norrmalmstorg bank robbery

Answer: stockholm syndrome


Question: Category: HISTORIC PEOPLE 
Clue: After his 1955 death, his papers were given to Jerusalem's Hebrew Univ. & his violin was left to his grandson

Answer: albert einstein


Question: Category: IN THE NEWS 
Clue: The U.N. designated October 12, 1999 as the date the Earth's population reached this figure

Answer:
6 billion