Read the following passage and mark letter A, B, C, or D to indicate the correct word that best completes each blank.

The Great Barrier Reef is the earth’s ___(1)___ reef system. At a length of over 2,500 km it is the largest ___(2)___ structure. You can even see it from space. However, the reef is in danger of dying. Because of global warming, the temperature in the atmosphere keeps rising. This also affects the water temperature. When the oceans get too warm the colorful reefs turn grey and die. The reef is also dying ___(3)___ pollution ___(4)___ by factories on the Australian and Indonesian coasts.
It’s a pity that we don’t care about the environment the ways the Aborigines did thousands of years ago. They respected nature, the animals and plants around them. They never killed more animals than they could eat. However, when Europeans arrived in Australia they destroyed a lot of things ___(5)___ the Aborigines valued.