2015最新GRE阅读每日一练（11月13日）

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每日一练

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.

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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