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There are thousands of coral reefs(珊瑚礁) in the world; Unfortunately, however, they are now in serious danger. More than one-third are in such bad shape that they could die within ten years.       Here are the three main causes discovered.
The first cause is pollution on land. The pollutants run with rainwater into rivers and streams, which carry the poisons into the ocean.     So they will be easily infected(感染) with diseases.
    Higher ocean temperatures kill the important food source(来源) for the coral—the algae, the tiny greenish-gold water plants that live on coral.     This process has happened more and more frequently in recent years.
The last factor contributing to the disappearance of coral reefs is people. People sometimes crash into reefs with their boats, breaking off large blocks of coral.     Moreover, some people even break coral off to collect for souvenirs since it is so colorful and pretty.

A．Global warming is another reason.

B．Many might not even last that long!

C．Divers who walk on reefs can also do serious damage.

D．Reefs provide a home for 25% of the fish in the ocean.

E. Chemicals from the poisons kill reefs or make them weak.
F. Steps must be taken now to stop over-fishing and pollution of the oceans.
G. When the algae die, the coral loses its color and it also dies in the end.