Mekong, Tiber and Danube.
The metric unit for Mass is a gram
Desertification <span>is the persistent degradation of dryland ecosystems by variations in climate and human activities.</span>
The Great Barrier Reef is special because it is by far the largest reef in the world. It is consisted of around 2,900 individual reefs. The size of this reef is approximately as the size of Germany. There are over 900 islands that are stretched over 2,600 km along the the reef. The Great Barrier Reef is so marking and big, that even though it is below water it can actually be seen from space. The ecological importance of this reef is enormous as it is a home for thousands of species, with approximately 10% of all fish species in the world living in it. Because of its beauty and numerous attractions, the Great Barrier Reef is one of the most visited tourist destinations, and the Australian economy manages to generate between 5 and 6 billion Australian Dollars annually from it. Unfortunately, all of the human activity has been affecting this reef very negatively, and little by little part of it is dying out.
