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30. One of the most urgent environmental problems in the world today is the shortage of clean water. (Câu đầu tiên)
31. It contains a rich variety of animals and plants, including 1,300 rare species that do not exist anywhere else in the world. (Dòng 3 -> 5 đoạn 2)
32. 50% hoặc It is the dumping ground for 50% of all marine pollution. (The Mediterranean Sea occupies....marine pollution)

$30$ `:` One of the most urgent environmental problems in the world today is the shortage of clean water.

Dẫn chứng `:` Câu đầu tiên

$31$ `:` It contains a rich variety of animals and plants, including 1,300 rare species that do not exist anywhere else in the world. 

Dẫn chứng `:` Câu thứ `3`

$32$ `:` `50%` hoặc It is the dumping ground for `50%` of all marine pollution.

Dẫn chứng `:` The Mediterranean Sea occupies....marine pollution.