Title: Opcional

Text: Thomas Edison tried two thousand different materials in search of a filament for the light bulb. When none worked satisfactorily, his assistant complained, "All our work is in vain. We have learned nothing." Edison replied very confidently, "Oh, we have come a long way and we have learned a lot. We know that there are two thousand elements which we cannot use to make a good light bulb." Cada párrafo será una prueba.

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