OG1 阅读 Q23

Choice D is the best answer. The authors explain that hydrogen bonds join together pairs of nitrogenous bases, and that these bases have a specific structure that leads to the pairing:"One member of a pair must be a purine and the other a pyrimidine in order to bridge between the two chains" (lines 27-29,"One...for"). Given the specific chemical properties of a nitrogenous base, it would be inaccurate to call the process random.
Choice A is incorrect because (lines 5-6,"To...possible") describe how nitrogenous bases attach to sugar but not how those bases pair with one another. Choice B is incorrect because (lines 9-10,"So...of") do not contradict the student's claim. Choice C is incorrect because (lines 23-25,"The...only") describe how the two molecules'chains are linked, not what the specific pairing between nitrogenous bases is.