请求解答新东方补充材料

saiko13

Nearly a century ago, biologists found that if they separated an invertebrate animal embryo into two parts at an early stage of its life, it would survive and develop as two normal embryos. This led them to believe that the cells in the early embryo are undetermined in the sense that each cell has the potential to develop in a variety of different ways. Later biologists found that the situation was not so simple. It matters in which plane the embryo is cut. If it is cut in a plane different from the one used by the early investigators, it will not form two whole embryos.
A debate arose over what exactly was happening. Which embryo cells are determined, just when do they become irreversibly committed to their fates, and what are the “morphogenetic determined” that tell a cell what to become? But the debate could not be resolved because no one was able to ask the crucial questions in a form in which they could be pursued productively. Recent discoveries in molecular biology, however, have opened up prospects for a resolution of the debate. Now investigators think they know at least some of the molecules that act as morphogenetic determinants in early development. They have been able to show that, in a sense, cell determination begins even before an egg is fertilized.
Studying sea urchins, biologist Paul Gross found that an unfertilized egg contains substances that function as morphogenetic determinants. They are located in the cytoplasm of the egg cell; i.e. in that part of the cell’s protoplasm that lies outside of the nucleus. In the unfertilized egg, the substances are inactive and are not distributed homogeneously. When the egg is fertilized, the substances become active and, presumably, govern the behavior of the genes they interact with. Since the substances are unevenly distributed in the egg, when the egg is fertilized egg divides, the resulting cells are different from the start and so can be qualitatively different in their own gene activity.
The substances that gross studied are maternal messenger RNA’s—products of certain of the maternal genes. He and other biologists studying a wide variety of organisms have found that these particular RNA’s direct, in large part, the synthesis of histone, a class of proteins that bind to DNA. Once synthesized, the histones move into the cell nucleus, where section of DNA wrap around them to form a structure that resembles beads, or knots, on a string. The beads are DNA segments wrapped around the histones; the string is the intervening DNA. And it is the structure of these beaded DNA strings that guides the fate of the cells in which they are located.
It can be inferred from the passage that the morphogenetic 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
C inactive until the embryo cells become irreversibly committed to their final function
D 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

我选的是D； 正确答案是E
为什么是选E  ,是怎么做的希望各位能为我解惑

edwardelric

本题是推断题，是要在理解全文的基础上推出的，d不正确identical to those明显错误
e， 你通读全文也没有直接对应点
本题重在理解，形态的决定~morphogenetic determinants
文章在第一段说了Nearly a century ago, biologists found that if they separated an invertebrate animal embryo into two parts at an early stage of its life, it would survive and develop as two normal embryos.
就这句就是e的直接推断的根据~
1个切产生两个不同的~在后文又没有否定本观点，只是It matters in which plane the embryo is cut. If it is cut in a plane different from the one used by the early investigators, it will not form two whole embryos.
说以数量上还是要多的
这样的推断很少见，需要太多我们的推测，但在蓝皮300上却挺多的

saiko13

谢谢你···我明白了···