智慧上进2021理综四答案

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Dear JohnI' m more than excited to know that you're going to visit my city soon. As for the traffic here. now I'd like toshare something about it with youWith various means of public transport, the traffic here is really convenient. Apart from the traditional publictransport such as buses, subways and taxis, which are always available, shared bikes and shared cars have becomemore and more popular recently. You can go almost everywhere you want just by using a smartphone. However,like most big cities, the rush hours can be extremely terrible.When you arrive, youd better take a subway to your hotel, because it's quite fast and cheap. But when yout around within the city, it all depends on your purpose and time. For example, shared bikes can be a perfect toolfor you to explore the tourist attractions like wide and Narrow AlleyTell me when you come. I' m looking forward to seeing youBest wishesYou

7.B【解析】亲代噬菌体只为子代噬菌体提供DNA模板,合成子代噬菌体所需的原料均来白大肠杆菌,甲组实验”S标记的是大肠杆菌的蛋白质(氨基酸),子代噬菌体蛋白质均被标记,乙组实验P标记的是亲代噬菌体的DNA,由于DNA复制方式为半保留复制,因此乙组子代中只有少量具有放射性,A正确;搅拌的日的是让吸附在大肠杆菌表面的噬菌体(蛋白质外壳)与大肠杆菌分离开来,而乙组实验的隙菌体蛋白质外壳不含放射性,故乙组实验中若搅拌不充分,不影响实验现象,B错误;甲组标记的大肠杆菌,离心后大肠杆菌分布在沉淀物中,因此该组放射性主要分布在沉淀物中,乙组用P标记的是噬菌体的DNA,噬菌体侵染细菌时,DNA进入细菌并随着细菌离心到沉淀物中,因此该组的放射性也主要分布在沉淀物中,若培养时间过长,由于子代噬菌体的裂解释放,甲乙两组实验的上清液中的放射性均会增强,C正确;甲组标记的大肠杆菌,离心后会分布在沉淀物中,S(标记蛋白质)改为H(标记蛋白质和DNA),实验现象基本不变,D正确