GWD-TN24的31没讨论过，困惑了~~

休止符

Q31: TTGWD2-Q21:

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.

The information provided most strongly supports which of the following?

A.Telomerase is the only enzyme that is present in cancerous cells but absent from cells that are not actively dividing.

B.In children, the only body tissues from which telomerase is absent are those in which cells are not rapidly dividing.

C.The presence of telomerase in bone marrow is no indication of bone marrow cancer.

D.Cancer of the bone marrow develops more rapidly than cancer growing in any other kind of adult tissue.

E.The level of telomerase production is always higher in cancerous tissue than in noncancerous tissue.

选C   我分析下B，好像是第一句话的否命题，原文说Telomerase 出现（充分） 就一定是在 cells that are actively dividing（必要） 而B说telomerase is absent 那么一定是cells are not rapidly dividing.  否命题不一定正确  所以不能选B 请问NN是这样吗？
然后C  我实在没弄明白嘛儿回事。。。

ctkstarcraft

原文的推理：
Telomerase is produced only in actively dividing cells.
Bone marrow cells continually divide ---->Telomerase is produced in Bone marrow cells.
Cancer cells are rapidly dividing  ----->Telomeras is also produced in cancer cells.

选项B:
小孩身上唯一没有Telomeras的tissue是那些细胞没在rapidly divide的tissue.
这里需要区分 actively divide和rapidly divide,  actively divide不一定是rapidly divide, 但rapidly divide一定是actively divide. 也就是rapidly divide的范围要小。
所以b应该说成：In children, the only body tissues from which telomerase is absent are those in which cells are not actively dividing.

选项C:
骨髓细胞中出现Telomerase 并不表明已患上骨髓癌。
正确。 因为出现在骨髓细胞中的Telomerase有两个可能的来源：1. 癌细胞分裂 2.骨髓细胞本身分裂

休止符

原文的推理：
Telomerase is produced only in actively dividing cells.
Bone marrow cells continually divide ---->Telomerase is produced in Bone marrow cells.
Cancer cells are rapidly dividing  ----->Telomeras is also produced in cancer cells.

选项B:
小孩身上唯一没有Telomeras的tissue是那些细胞没在rapidly divide的tissue.
这里需要区分 actively divide和rapidly divide,  actively divide不一定是rapidly divide, 但rapidly divide一定是actively divide. 也就是rapidly divide的范围要小。
所以b应该说成：In children, the only body tissues from which telomerase is absent are those in which cells are not actively dividing.

选项C:
骨髓细胞中出现Telomerase 并不表明已患上骨髓癌。
正确。 因为出现在骨髓细胞中的Telomerase有两个可能的来源：1. 癌细胞分裂 2.骨髓细胞本身分裂

-- by 会员 ctkstarcraft (2010/2/25 15:00:27)

谢谢ctkstarcraft~不过我还是有点困惑该题充要性的问题，我也有注意到B的概念偷换，但如果就算B改成actively，我想清楚一下，这确实是原文的否命题，对吗？不过我记得新东方老师说了，support类的归纳题是可以出现否命题的，所以如果B改成了actively就可以算对，是吧？

liverpool123

换成active就对了

ctkstarcraft

B不是原文的否命题，而是逆否命题。
原文：
cells are actively dividing   --->  Telomera is produced
逆否：
Telomera is not produced(no Telomera)  ---> cells are not actively dividing

休止符

不对呀~~~only后面的才是必要条件  原文的推理应该是Telomerase is  produced -----》cells that are actively dividing才是。。。

ctkstarcraft

不对呀~~~only后面的才是必要条件  原文的推理应该是Telomerase is  produced -----》cells that are actively dividing才是。。。

-- by 会员 休止符 (2010/2/25 22:30:01)

你说得对，是必要条件，我看错了，是否命题。。。

edwinwos

讲得非常好

edwinwos

原文的推理：
Telomerase is produced only in actively dividing cells.
Bone marrow cells continually divide ---->Telomerase is produced in Bone marrow cells.
Cancer cells are rapidly dividing  ----->Telomeras is also produced in cancer cells.

选项B:
小孩身上唯一没有Telomeras的tissue是那些细胞没在rapidly divide的tissue.
这里需要区分 actively divide和rapidly divide,  actively divide不一定是rapidly divide, 但rapidly divide一定是actively divide. 也就是rapidly divide的范围要小。
所以b应该说成：In children, the only body tissues from which telomerase is absent are those in which cells are not actively dividing.

选项C:
骨髓细胞中出现Telomerase 并不表明已患上骨髓癌。
正确。 因为出现在骨髓细胞中的Telomerase有两个可能的来源：1. 癌细胞分裂 2.骨髓细胞本身分裂

-- by 会员 ctkstarcraft (2010/2/25 15:00:27)

讲得非常 明白！

咕咕鸡gogo加油

可是题目讲说--成年人的身体组织中往往缺乏这种酶， 但是有两个例外。一个是成年人的骨骼细胞，另一个是患癌症的成年人。 因为这两种情况细胞都是分裂的。 所以D选项中讲的--骨癌比其他部位的癌症发展扩散的更快。应该是对的啊。因为这种分裂酶既在骨骼中存在， 又在癌症中存在， 因此两者叠加必然比仅仅患癌症的要分裂得快啊。 请NN解释，跪求