题干

下列关于核酸以及基因的叙述中正确的是(   )

A:细胞中一定同时含有两种核酸,但只有DNA对遗传信息的表达有作用

B:真核细胞的基因位于染色体上,且染色体是由DNA和蛋白质组成

C:原核细胞中的DNA分子为环状,真核细胞中的DNA分子也有可能是环状

D:DNA分子的多样性与构成DNA分子的脱氧核苷酸的种类、数量、排列顺序以及脱氧核苷酸链的空间结构有关

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答案(点此获取答案解析)

C

同类题2

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    Some people are lucky enough to be born with a good sense of direction and even if they have only visited a place once, they will be able to find it again years later.

    I am one of those unfortunate people who have poor sense of direction and I may have visited a place time after time but I still get lost on my way there. When I was young I was so shy that I never dared ask complete strangers the way and so I used to wander round in circles and hope that by some chance I would get to the spot I was heading for.

    I am no longer too shy to ask people for direction, but I often receive replies that puzzle me. Often people do not like to admit that they didn't know their hometown and will insist on telling you the way, even if they do not know it; others, who are anxious to prove that they know their hometown very well, will give you a long list of directions which you can not possibly hope to remember, and still others do not seem to be able to tell between their left and their right and you find in the end that you are going in the opposite direction to that in which you should be going.

    If anyone ever asks me the way to somewhere, I always tell them I am a stranger to the town in order to avoid giving them wrong direction but even this can have embarrassing results.

    Once I was on my way to work when I was stopped by a man who asked me if I would direct him the way to the Sunlight Building. I gave my usual reply, but I had not walked on a few steps when I realized that he had asked for directions to my office building. However, at this point, I decide it was too late to turn back and search for him out of the crowd behind me as I was going to meet with someone at the office and I did not want to keep him waiting.

    Imagine my embarrassment when my secretary showed in the very man who had asked for directions of my office and his astonishment when he recognized me as the person he had asked.