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  3. Many people dream of having a smarter brain. Princeton neurobiologist Joseph Z. Tsien found the key. In September he announced

Many people dream of having a smarter brain. Princeton neurobiologist Joseph Z. Tsien found the key. In September he announced

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问题     Many people dream of having a smarter brain. Princeton
neurobiologist Joseph Z. Tsien found the key. In September he
announced that he built a better mouse by altering a gene that 【M1】______
affects learning and memory. A similar process of gene
manipulation might conceivably be used one day to boost up 【M2】______
intelligence in humans.
    The secret lies in a feature of brain cells which called the 【M3】______
nomda receptor, which Tsien likes to a cylindrical tube or window 【M4】______
that mediates the flow of information. When the window is open,
chemicals called neurotransmitters flow through easily and
memory is registered or stored. Tsien noticed that the receptor 【M5】______
worked more efficiently when teamed with the gene NR2B, so he
introduced extra NR2B genes into a batch of fertilized mouse eggs.
In a normal mouse, the memory window is open in just 【M6】______
150-thousandths of a second. In Tsien’s specifically engineered 【M7】______
mice, the window opens for 250-thousandths of a second, long
enough to make a remarkable impression in memory retention. 【M8】______
When he pitted his mice with common mice, they won paws down. 【M9】______
Ordinary mice could recognize a Lego block for 12 hours, but
smart mice could remember the block for up to three days. "That’s
a profound enhancement," Tsien says.
    Can it be done with humans? Maybe, so genetic engineering 【M10】______
will have to make some extraordinary advances first. And some
thorny ethical issues will have to be resolved. Meanwhile, Tsien
promises to keep his furry little geniuses locked up in a lab, far
from your larder. "Otherwise," he says, "you might need a smart cat
or a smart mousetrap to catch them."
【M10】
选项
答案so—but
解析 连词使用错误。so之后的从句与它前面的“或许可以”并没有因果关系，而应当是转折关系，即就算该试验可能用于人类也必须首先取得突破性进展以及解决棘手的道德问题。
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