题目内容：
Conservation or Wasted Effort?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.___________(46)
Energetic steps are being taken to preserve the black robin. ___________(47) The idea is to buy another island nearby as a special home, a "reserve", for threatened wild life, including black robins. The organizers say .that Little Mangere should then be restocked (重新准备) with the robin's fooD．Thousands of the required plants are at present being cultivated in New Zealand.
Is all this concern a waste of human effort? ___________(48) Are we losing our sense of what is reasonable and what is unreasonable?
In the earth's long, long past hundreds of kinds of creatures have evolved, risen to a degree of success and died out. In the long, long future there will be many new and different forms of life. Those creatures that adapt themselves successfully to what the earth offers will survive for a long time. ___________ (49) This is nature's proven method of operation.
The rule of selection---'the survival of the fittest"--is the one by which human beings have themselves arrived on the scene. We, being one of the most adaptable creatures the earth has yet produced, may last longer than most.___________ (50) You may take it as another rule that when, at last, human beings show signs of dying out, no other creature will extend a paw (爪) to postpone our departure. On the contrary, we will be hurried out.
Life seems to have grown too tough for black robins. I leave you to judge whether we should try to do anything about it.
A．Some creatures, certain small animals,insects and birds, will almost certainly outlast (比……长久) man, for they seem even more adaptable.
B．Those that fail to meet the challenges will disappear early.
C．Detailed studies are going on, and a public appeal for money has been made.
D．Both represent orders in the classification of life.
E. Is it any business of ours whether the black robin survives or dies out?
F. These are the only black robins left in the world.
请选择（46）处的最佳答案．
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