再请教一题
[font=Tahoma][size=9.5pt]Telomerase is an enzyme that is produced only in cells that are actively dividing.For this reason it is generally absent from body tissues in adults.
Bone marrow is an exception to this rule, however, since even in adults, bone marrow cells continually divide to replace old blood cells.
Cancers are another exception, because their cells are rapidly dividing.[/size][/font]
[font=Tahoma][size=9.5pt]The information provided most strongly supports which of the following?[/size][/font]
[font=Tahoma][size=9.5pt]A.
[/size][/font][font=Tahoma][size=9.5pt]Telomerase is the only enzyme that is present in cancerous cells but absent from cells that are not actively dividing.[/size][/font]
[font=Tahoma][size=9.5pt]B.
[/size][/font][font=Tahoma][size=9.5pt]In children, the only body tissues from which telomerase is absent are those in which cells are not rapidly dividing.[/size][/font]
[font=Tahoma][size=9.5pt]C.
[/size][/font][font=Tahoma][size=9.5pt]The presence of telomerase in bone marrow is no indication of bone marrow cancer.[/size][/font]
[font=Tahoma][size=9.5pt]D.
[/size][/font][font=Tahoma][size=9.5pt]Cancer of the bone marrow develops more rapidly than cancer growing in any other kind of adult tissue.[/size][/font]
[font=Tahoma][size=9.5pt]The level of telomerase production is always higher in cancerous tissue than in noncancerous tissu[/size][/font]
[font=Tahoma][size=9.5pt]答案选c 既然骨髓细胞的更新产生T，癌细胞的分裂也产生T，那为什么能说在骨髓中发现的T就一定不是源自骨髓癌的呢？[/size][/font] C 不是说“在骨髓中发现的T就一定不是源自骨髓癌的”，而只是说不能根据骨髓里面有 telomerase 而说是患了骨髓癌。
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