Use reasoning to lead to the answer of the following question:
Where can you look up a number to a business when you don't have electricity?\nOptions:\n- power grid\n- equation\n- telephone book\n- math problem\n- roulette wheel
 Reasoning process:
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A telephone book is accesible evn when there is no electricty. A telephone book has numbers of various businesses. Therefore, the final answer is telephone book.
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