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In laboratories, healthy adult human brain neuronstypically live no more

than a few hours, makingextensive research impossible. Furthermore,scientists'

inability to reproduce healthy neuronshas prevented the use of neurons in

experimentaltreatments of severe neurological disorders.

However, two researchers at the Johns HopkinsUniversity School of Medicine

have successfully maintained mature, human brain neurons inlong-term cultures by

using cells obtained during surgery on an 18-month-old victim ofunilateral

megalencephaly. The rare disorder, in which one side of the brain grows

substantiallylarger than the other, occurs when neurons in the abnormal

hemisphere undergo too manycell divisions before they mature. The neuronal

imbalance in the brain of the infant causedseizures, prompting surgeons to

remove the enlarged hemisphere---a treatment that hasproven successful in

similar cases. The researchers then took neurons from the excised brainmatter

and placed them in a blood-rich culture medium. After days, many of the cells

had died,but a few continued to grow and divide. Nineteen months later, the team

had subculturedcolonies of neurons onto new culture plates more than 20 times,

with no significant changes incellular appearance or growth characteristics.

Scientists still don't know what triggers the proliferation of neurons in

unilateralmegalencephaly. The neurons cultivated at Johns Hopkins---unlike those

culled from tumorsare not cancerous, and accordingly are much more valuable as

research tools. Finally, theexperiment presents the possibility that such

neurons could be used in experimentaltreatments that currently use fetal brain

cells, sidestepping an uncomfortable ethical issue.

Which sentence in the second paragraph, in which the author makes a

conclusion, isnot supported with any factual or anecdotal evidence?

A.will allow researchers to expand their knowledge of neurological

workings

B.is necessary to cure unilateral megalencephaly

C.is a viable medical procedure in some cases

D.is usually performed on infants who suffer from unilateral

megalencephaly

E.is a rare procedure that is performed as a last resort

The passage supplies information to answer which of the following

questions?

A.How old is the average unilateral megalencephaly patient?

B.Can fetal brain cells be used to treat unilateral megalencephaly?

C.Have scientists found a way to allow cells from victims of unilateral

megalencephaly to existoutside of the body?

D.How long can neurons culled from tumors be sustained outside the

body?

E.Will scientists find further experimental uses for neurons culled from

unilateralmegalencephaly victims?

In the second paragraph, select the sentence in which a term is introduced

thatrequires elucidation in a later sentence.

正确答案

1C

2C

3However, two researchers at theJohns Hopkins University School of

Medicinehave successfully maintained mature, humanbrain neurons in long-term

cultures by usingcells obtained during surgery on an 18-month-old victim of

unilateral megalencephaly.

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