25. It can be inferred from the passage that the morphogent'tic determinants present in the early embryo are
(A) located in the nucleus of the embryo cells
(B) evenly distributed unless the embryo is not developing normally I
(C) inactive until the embryo cells become irreversibly committed to their final function
(0) identical to those that were already present in the unfertilized egg
(E) present in larger quantities than is necessary for , the development of a single individual :
The best answer is E. The socond and third paragraphs of the ; passage indicate that morphogenetic determinants are sub- , stances in the embryo that are activated after the egg has been fertilized and that "tell a cell what to become" (lines 15-16). If, as tb(; author asserts in the first paragraph, biologists have succeeded in dividing an embryo into two parts, each of which survives and develops into a normal embryo, it can be concluded that the quantity of morphogenetic detenninants in the early embryo is greater than that required for the development of a single individual. Choices A, B, and C are directly contradicted by information in the passage, and D makes an assertion that cannot be inferred from the passage.
答案为什么是E？ 她给的解释不是很能读懂。 谢谢！作者: himba 时间: 2004-7-27 15:25
这个是很难很难的.
25. It can be inferred from the passage that the morphogent'tic determinants present in the early embryo are
(A) located in the nucleus of the embryo cells 这个不对,不在细胞核里头
(B) evenly distributed unless the embryo is not developing normally I 不对,明确说是not evenly
(C) inactive until the embryo cells become irreversibly committed to their final <I>function</I> 时间上的分水岭是fertilized or not,这个也不对
(0) identical to those that were already present in the unfertilized egg 这个不对,that the morphogent'tic determinants present in the early embryo 应该是不同的.至少可以找到有发展
(E) present in larger quantities than is necessary for , the development of a single individual :
只有e有味道.就是第一段.科学家分开受精卵而能够发育为两个独立的胚胎,吧e取非,就和文章矛盾了.所以e对.
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