[单选题]

Can Gene TechnologyMake Human Smarter?

Almost everyonewants to get smarter. To achieve that,some choose to do exercise,others chooseto take in more nutritions good for brains.Princeton neurobiologist Joseph

Z.Tsien possiblyfound a different way to make it. In September he announced that he'd built abetter mouse by altering a gene that affects learning and memory.A similar

process of genemanipulation might conceivably be used one day to boost intelligence in humans.

The key of thistechnology lies in a feature of brain cells called the NMDA receptor,whichTsien likens to a cylindrical tube or window that mediates the flow of

information.When thewindow is open,chemicals called neurotransmitters flow through easily andmemory is registered and stored. But as organisms mature,the window

begins toclose.(This may explain why children lose their facility for learning newlanguages when they reach sexual maturity and why some people suffer memoryloss as

they age.)

Tsien also found outthat the receptor worked more efficiently if it is teamed with the gene NR2B,sohe introduced extra NR2B genes into a batch of fertilized mouse eggs.In

a normal mouse,thememory window is open for just 150-thousandths of a second.In Tsien's speciallyengineered mice,the window opens for 250-thousandths of a

second,long enoughto make a remarkable difference in memory retention.When he pitted his miceagainst common mice,they won paws down.Ordinary mice could

recognize a Legoblock for 12 hours,but smart mice could remember the block for up to threedays."That's a profound enhancement,"Tsien says.

Can this technologybe applied to humans?Maybe,but genetic engineering will have to make someextraordinary advances first. And some thorny ethical issues will have to

be resolved.Mean-while,Tsien promises to keep his furry little geniuses locked up in alab,far from your larder. "Otherwise,"he says,"you might need asmart cat or a smart

mousetrap to catchthem."Why do some old peopleare likely to lose their memory?

A.As one's organismmature,the window for memory is likely to close.

B.There is notenough nutrition in their brains.

C.They haveremembered too much inftrmation.

D.The cells in theirbrains are getting too old to store much information.

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