Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

   Not much is known about the saola, a mysterious horned mammal native to forests in the Annamite Mountains of Laos and Vietnam. The species was unknown to Western science until 1992, when researchers encountered saola horns in the home of a local hunter. Scientists have only managed to record a saola in the wild five times and only with camera traps. At least one thing seems fairly certain, though: The saola is a very endangered species. 

   Adult saolas are about 33 inches tall at the shoulder, but they can weigh 220 pounds, and their two long horns can grow to 20 inches. Smaller than most cattle and bison, they have managed to hide from humans better than other animals at their size. They are likely the world's largest land animal that has never been seen in the wild by a biologist. Even so, they are still suffering the effects of human's presence. 

   Hunting is the main danger to the saolas, even though most hunters in the species' range have little interest in killing or capturing them. Unlike many other animals in their habitat, the saolas are not featured in the traditional Chinese pharmacopeia, so there isn't much financial incentive for hunters to target saolas for export. The species' meat is not considered especially appealing compared with other, more common ungulates in the same forests, like muntjacs or sambar deer, so they are not highly valued as bushmeat, either. Nonetheless, they're often incidentally killed amid the general pursuit of other wildlife. Some saolas fall victim to bushmeat hunters, but the main threat comes from wire traps set by professional poachers. 

   Another major threat to the saola is a familiar one for wildlife all over the world: the loss and fragmentation of its habitat. The development of the Ho Chi Minh Highway has already affected saola populations by fragmenting forests as well as by increasing human access for logging, hunting, and spiriting wildlife away to urban markets. The road has also led to more deforestation in several key areas for the saola, especially the Hue Saola Nature Reserve and Quang Nam Saola Reserve. The high growth rate in human populations will likely add to the pressures already fueling the saola's decline. 

   People have been trying to capture saolas about 20 times since 1992. Unfortunately, all have died shortly afterward except for two that were released back into the wild. There are currently no captive saolas anywhere, and thus no backup for wild populations. If a captive breeding program can't be established before the last wild saolas fade away, the species will be lost forever. 

(Adapted from https://www.treehugger.com) 

What is the passage mainly about?