第41篇,第6题
                

.6. According to the passage, researchers working under the   two-category hypothesis were correct in thinking that

  (A) prokaryotes form a coherent group

  (B) the common ancestor of all living things had complex      properties

  (C) eukaryotes are fundamentally different from true bacteria

  (D) true bacteria are just as complex as eukaryotes

  (E) ancestral versions of eukaryotic genes functioned      differently from their modern counterparts.

为什么A不对? 文中有

These techniques have strongly

   suggested that although the true bacteria indeed form a     

   large coherent group, certain other bacteria, the archaebac-

   teria, which are also prokaryotes and which resemble true

(40)
                bacteria, represent a distinct evolutionary branch that

   far antedates the common ancestor of all true bacteria.

Passage 41

  It was once assumed that all living things could be

  divided into two fundamental and exhaustive categories. Multicellular plants and animals, as well as many unicellu-

lar organisms, are eukaryotic—their large, complex cells

(5) have a well-formed nucles and many organelles. On the

  other hand, the true bacteria are prokaryotic cell, which

  are simple and lack a nucleus. The distinction between

  eukaryotes and bacteria, initially defined in terms of

  subcellular structures visible with a microscope, was ulti-

(10)
                mately carried to the molecular level. Here
            prokaryotic and

   eukaryotic cells have many features in common. For

  instance, they translate genetic information into proteins

  according to the same type of genetic coding. But even

  where the molecular processes are the same, the details in

(15)
                the two forms are different and characteristic of the respec-

   tive forms. For example, the amino acid sequences of vari-

   ous enzymes tend to be typically prokaryotic or eukaryotic.

  The differences between the groups and the similarities

  within each group made it seem certain to most biologists

(20)        that the tree of life had only two stems. Moreover, argu-

ments pointing out the extent of both structural and func-

tional differences between eukaryotes and true bacteria

convinced many biologists that the precursors of the

   eukaryotes must have diverged from the common

(25)        ancestor before the bacteria arose.

  Although much of this picture has been sustained by

more recent research, it seems fundamentally wrong in one

 respect. Among the bacteria, there are organisms that are

 significantly different both from the cells of eukaryotes and

(30)
                from the true bacteria, and it now appears that there are  

  three stems in the tree of life. New techniques for deter-

 mining the molecular sequence of the RNA of organisms

have produced evolutionary information about the degree

to which organisms are related, the time since they diverged

(35)
                from a common ancestor, and the reconstruction of ances-

   tral versions of genes. These techniques have strongly

   suggested that although the true bacteria indeed form a     

   large coherent group, certain other bacteria, the archaebac-

   teria, which are also prokaryotes and which resemble true

(40)
                bacteria, represent a distinct evolutionary branch that

   far antedates the common ancestor of all true bacteria.