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You answered "Pebbles". Click "CONTINUE" to proceed to the next question.
Interesting fact:
'Trying to understand the way nature works involves a most terrible test of human reasoning ability. It involves subtle trickery, beautiful tightropes of logic on which one has to walk in order not to make a mistake in predicting what will happen. The quantum mechanical and the relativity ideas are examples of this.' — Richard P. Feynman