450)=450"> 本文选自雅思听力Section 4，难度较大 HINTS 18-29℃ Tropics of Cancer Capricorn 全文听写，英式拼法 订阅节目更方便
Coral is actually the exoskeletons of coral polyps. Made of limestone, these skeletons build up over time, forming the reef. New corals are born each April. At a certain hour, on a certain night, mature corals suddenly release clouds of eggs and sperm into the sea. After the fertilized eggs take root on the seafloor, they can grow up to 15 centimetres per year. Coral reefs are present in the waters of over 100 countries. These are warm 18-29℃, shallow, sunny regions primarily between the Tropics of Cancer and Capricorn. Only clear, warm salt water can support a coral reef. And because sunlight is crucial to the reef's survival, the water must also be shallow. The algae that grow on coral provide much of the coral's food. In deeper water, algae cannot get the sunlight they need to grow.