In the following passage some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank.

Among the largest species of cats in the world, tigers are powerful hunters with (1)________
teeth, strong jaws and agile bodies. They range across Asia from Russia all the way to
Sumatra and mainland Southeast Asia. Researchers still have much to learn (2) ________
these beautiful, endangered (3) ________.
There is currently one recognized species of tiger, Panthera tigris. Scientists have further (4)
________ the tiger into nine subspecies: the extinct Bali, Caspian and Javan subspecies, and
the living Malayan, Sumatran, South China, Indochinese, Bengal and Amur (or Siberian)
subspecies. Of these six subspecies, AZA-accredited zoos currently manage three: Amur,
Malayan, and Sumatran. The Smithsonian's National Zoo and Conservation Biology Institute
is home to Sumatran and Amur tigers; Sumatran tigers are (5) ________ as Critically
Endangered on the International Union for Conservation of Nature's Red List, and Amur tigers
have been classified as Endangered.