题目

  Like all big cities, Paris has a traffic problem: lots of cars, lots of traffic jams(阻塞) and lots of pollution from exhaust fumes(废气). So the city began a scheme(计划) to improve the situation. Under the Velib scheme(‘Velib’ comes from velo liberte, or ‘bicycle freedom’) , people can take a bicycle, use it for as long as they want, and then leave it at the same or another bicycle station. The first half-hour on the bike is free, but if you don’t return it after 30 minutes, you have to pay. But it’s only ∈1 a day or ∈29 a year! The bicycles are heavy (25 k3．下列关于cDNA文库及其建立过程的叙述中，哪一项是不正确的（　　）A．cDNA文库包含了某种生物的部分基因B．需从特定组织或细胞中提取DNA或RNAC．利用mRNA的反转录合成互补DNA片段D．合成的互补DNA片段需要连接在载体上