OG1 阅读 Q27

Choice D is the best answer. The authors explain how the DNA molecule contains a "precise sequence of bases" (lines 43-44"possible...the"), and that the authors can use the order of bases on one chain to determine the order of bases on the other chain: "If the actual order of the bases on one of the pair of chains were given, one could write down the exact order of the bases on the other one, because of the specific pairing. Thus one chain is, as it were, the comple-ment of the other, and it is this feature which suggests how the deoxyribo-nucleic acid molecule might duplicate itself" (lines 45-51"genetical ...itself"). The authors use the words "exact," "specific," and "complement" in these lines to suggest that the base pairings along a DNA chain is understood and predictable, and may explain how DNA "duplicate[s] itself" (line 51"acid ...itself").Choice A is incorrect because the passage does not suggest that most nucle-otide sequences are known. Choice B is incorrect because these lines are not discussing the random nature of the base sequence along one chain of DNA.
Choice C is incorrect because the authors are describing the bases attached only to the sugar, not to the sugar-phosphate backbone.