单选题 23. Some conservationists, concerned about the rapid depletion through poaching of elephant herds in certain parts of Africa, are urging countries to which ivory is sold to ban ivory importation. This ban, they argue, would prevent ivory sellers from reaching their market, and elephant herds would have a chance to recover.
The conservationists' recommendation as described is based on which of the following assumptions? ______

A、 The capacity of any illegal channels that may exist for the sale of ivory in export markets cannot expand to meet demand in those markets.
B、 There now exist synthetic substitutes for ivory that are essentially indistinguishable from the natural product.
C、 Bans on imports of ivory need to be combined with intensified efforts to stop poaching in order to be effective.
D、 To the economies of those countries that have significant elephant herds, elephants are more valuable alive than dead.
E、 In some parts of Africa where poaching has depleted elephant herds, those herds are already beyond recovery.

【正确答案】 A

【答案解析】 A：选项取反。出口市场可以扩充产能来满足需求→尽管象牙无法进口了，但是出口市场扩大了→大象种群依然会受到破坏，削弱原文，正确。
B：与天然象牙差别不大的人工合成品本身就能减少象牙的进口和销售，因此意味着不需要禁止象牙进口。选项本身就在削弱原文，不选。
C：选项取反。禁止象牙进口不需要和阻止偷猎相结合就能有效，加强原文，不选。
D：依靠活着的大象来发展经济的国家应该属于象牙出口国，而文章讨论的是禁止进口，与本文无关，不选。
E：该选项本身在削弱原文，不选。