<span>On November 19, 1493 Puerto Rico was discovered by Christopher Columbus on his second voyage to claim lands for the rulers of Spain, King Ferdinand and Queen Isabella. In 1493 the island was called Borinquen by the indians who lived there. Columbus named it San Juan Bautista.</span>
Scientists think that algae first evolved approximately 2.7 billion years ago, and soon after this oxygen began to exist in the atmosphere. Photosynthesis by primitive plants and algae released oxygen, which gradually built up in the atmosphere.
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¿Qué es la página 15 y 16? ¿Puedes mostrarnos?
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1. maintain/keep
2. be certain of something or be sure of something
3. creators
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