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Great Barrier Reef

The Great Barrier Reef is made of coral, a colorful rock-like substance actually composed of many small marine animals, each one less than half a centimeter in size. Coral grows in colonies that can reach over a meter and a half in height, and several of these colonies grow in close proximity to each other, eventually joining up to form an underwater chain or reef. The Great Barrier Reef refers to a series of almost three thousand coral reefs that stretch across the ocean floor in a twelve hundred mile chain, which makes it so long that it can actually be seen from space. Apart from its size, the Great Barrier Reef is also renowned for its age. The living part of the reef itself is around 8,000 years old, but sits atop the remains of dead coral that is much older, in some places almost half a million years old. A system of living organisms so anc ient and so large would be fascinating to scientists by the simple fact of
A. sharks.
B. sponges.
C. anemones.
D. whales.

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