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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. "
【B4】
选项 A、without
B、through
C、despite
D、after
答案A
解析 介词辨析题。依据第二段第二句相关内容，一半实验鼠服用了记忆阻断的药物后，由于最后听到嘟嘟声是在药物的干预之下，不再害怕这种声音。由此可以反推，这些老鼠最后听到嘟嘟声时，应该没有电击，否则它们仍会对这种声音感到恐惧，故此处所选介词应表示否定意义，因此[A]without为正确答案。根据上述分析，可首先排除表示方式和时间关系的[B]through和[D]before；根据第二句中逗号前后的句意可以判断，此处不是包含或类比关系；而[C]despite表示“虽然，尽管”，表达的是让步关系，故也应排除。
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