The correct answers are:
1. Mariana Trench - the deepest ocean depth in the world is found here;
Located near the North Mariana Islands, the Mariana Trench is a place where the Eurasian, Philippine, and Pacific plates have their boundary, which contributed to this incredibly deep crack in the ocean crust.
2. Archipelago - chain of islands;
Archipelago is a term that is used for a chain of islands, made in the same way by the same factors, and usually they are in close proximity,even though there's exceptions.
3. Great Barrier Reef - Australia's natural wonder that can be seen from space;
This is the biggest coral reef in the whole world, and it stretches along the eastern and northeastern coast of Australia;
4. Ring of Fire - D. 75 percent of the world's active volcanoes are located here;
The Ring of Fire is located alongside the boundary of the Pacific plate with the other plates, and since there's subduction zones all over its boundary, there's lots of active volcanoes.