单选题
【填句补文】The black robin（旅鸫）is one of the world's rarest birds. It is a small, wild bird, and it lives only on the island of Little Mangere, off the coast of New Zealand. In 1967 there were about fifty black robins there; in 1977 there were fewer than ten. ________.
A、These are the only black robins left in the world.
B、Those that fail to meet the challenges will disappear early.
C、Both represent orders in the classification of life.
D、Detailed studies are going on, and a public appeal for money has been made.