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  3. Researchers led by New York University neuroscientist Joseph LeDoux recently claimed to be the first scientists to erase a singl

Researchers led by New York University neuroscientist Joseph LeDoux recently claimed to be the first scientists to erase a singl

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问题     Researchers led by New York University neuroscientist Joseph LeDoux recently claimed to be the first scientists to erase a single memory. Working with rats, LeDoux’s team first【B1】______the animals to fear both a beep and a siren【B2】______giving them an electric shock every time either of the tones sounded. Then LeDoux gave half the rats the drug U0126, which is known to【B3】______with memory storage, and replayed the beep【B4】______electric shocks.
    A day later, when LeDoux【B5】______back both tones to the rats, the animals that hadn’t been given the drug were still fearful of both sounds.【B6】______the rats that had been given the memory-blocking drug weren’t【B7】______of the beep, which they had last heard while【B8】______the influence of U0126.
    【B9】______how U0126 exerts its amnesiac effect is【B10】______, but it may block the synthesis of proteins that help strengthen【B11】______between neurons and establish memories. The opportunity for erasure【B12】______during the act of retrieving a memory, because that’s【B13】______the memory is being updated and【B14】______again for long-term storage. " Only those memories that are activated are【B15】______," LeDoux says.
    Drugs like U0126 may someday【B16】______sufferers of traumatic memories. A small group of human studies have been done on a drug called propranolol, which blocks the action of stress neurotransmitters that help【B17】______memories in the brain, but LeDoux’s work shows the【B18】______for greater precision. " You might be able to【B19】______the traumatic impact of memories in people," says LeDoux. " The good news is you wouldn’t be【B20】______off their memory bank. "
【B6】
选项 A、Though
B、And
C、But
D、Since
答案C
解析 连词辨析题。本题考查句子之间的逻辑关系。空格所在句指出当没有服用药物的老鼠听到两种声音时，仍然感到害怕；本空之后的分句则谈到服用记忆阻隔药物的老鼠对嘟嘟声的反应。根据前文所述，研究者可以消除单个记忆，可见老鼠应不再记得听到嘟嘟声时曾遭电击，也就对嘟嘟声不再害怕。故前后两句是对照或转折关系，故[C]But为正确答案。根据句间关系的分析，可首先排除表示顺接关系的[B]And和表示时间关系或因果关系的[D]Since；而[A]Though表示让步，因此也应排除。
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