Subspecies are often difficult to distinguish from one another .
区分不同的亚种是很困难的。
All five remaining tiger subspecies are endangered , and many protection programs are in place .
现存的5个老虎亚种都濒临灭绝，因此很多保护项目都在紧锣密鼓的进行中。
There were once eight tiger subspecies , but three became extinct during the 20th century .
老虎曾经有过一共8个亚种，但其中三个亚种在20世纪灭绝。
The sumatran rhinoceros is thought to have gone extinct in thailand and peninsular malaysia due to poachers working in crime rings , and two subspecies of african rhino have suffered similar fates .
