请阅读Passage 1。完成第小题。
Passage 1
African elephants have been slaughtered at alarming rate over the past decade, largely because they are the primary source of the world's ivory. Their population has been dwindled from 1.3 million in 1979 to just 625,000 today, and the rate of killing has been accelerating in recent years because many of the older, bigger tusked animals have already been destroyed. "The poachers now must kill times as many elephants to get the same quantity of ivory," explained Curtis Bohlen,Senior vice president of the World Wildlife Fund.
Though its record on the environment has been spotty so far, the government last week took the lead in a major conservation issue by imposing a ban on ivory imports into the US. The move came just four days after a consortium of conservation groups, including the World Wildlife Fund and Wildlife Conservation International, called for that kind of action, and it made the US the first nation to forbid imports of both raw and finished ivory. The ban, says Bohlen, sends a very clear message to the ivory poachers that the game is over.
In the past African nations have resisted an ivory ban, but increasingly they realized that the decimation of the elephant herds poses a serious threat to their tourist business. Last month Tanzania and several other African countries called for an amendment to the 102 nation Convention on International Trade in Endangered Species that would make the ivory trade illegal worldwide.
The amendment is expected to be approved at an October meeting in Geneva and to go into effect next January. But between now and then, conservationists contend, poachers may go on a rampage,killing elephants wholesale, so nations should unilaterally forbid imports right away. The US government brought that argument, and by week's end the twelve nations European Community had followed with its own ban.
According to the passage, "dwindle" (Para.1) means__________.
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A.decrease
B.enlarge
C.weaken
D.eliminate