题目

女性子宫肌瘤细胞中最长的DNA分子可达36mm，DNA复制速度约为4um/min，但复制过程仅需40min左右即完成．这是因为DNA分子（ ） A．边解旋边复制 B．每个复制点双向复制，使子链迅速延伸 C．以半保留方式复制 D．复制起点多，分段同时复制 答案：解：由题意知，长为36mmDNA分子进行复制，如果只从一个位点复制需要的时间是36×1000÷4=9000分钟，而实际复制过程中只需要40min左右即完成，由此可以推出该DNA分子复制时具有多个起点，多个起点同时分段复制． 故选：D．阅读理解 　　Have you ever wondered how some people can break bricks with their bare hands? People who can do this kind of thing are experts in Karate(空手道). They are called“Karatekas”. Let's try to find out how Karatekas could do such things. We wanted to learn if they were especially strong and we go some surprising answers! Believe it or not, Karatekas aren't stronger than ordinary people——they just have more courage! 　　A Karate expert strikes hard objects like bricks or plates with the small bone in his wrist, opposite the thumb. Speed is the essence(实质)of this sport. But the strange thing that untrained men can break hard objects in the same way just as well as Karatekas Of course, Karatekas practise a lot and they have a layer of hard skin round their wrists. Though they have this advantage over ordinary people, it's basically just a question of willpower(毅力)——at least, that's what you cant ell your mother after you've experimented on a few dinner plates! (1)Who can break bricks with their bare hands? [　　] A．Only experts in Karate. B．People are especially stronger. C．People have a layer of hard skin round their wrists. D．People have more courage. (2)The essence of Karate is ________. [　　] A．speed　　　　　B．courage C．training　　　　D．hard skin (3)What advantage do Karatekas have over ordinary people? [　　] A．They have a layer or hard skin round their wrists. B．They practise a lot. C．The do this kind of thing in a different way. D．They are especially strong. (4)Which of the following sayings best describes the main idea of the passage? [　　] A．Respect a man, he will do the more. B．Where there is a will, there is a way. C．Self-preservation is the first law of nature. D．Knowledge without practice makes but half an artist.