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问题 单项选择题

以RNA做模板，催化合成cDNA第一条链的酶是

A．反转录酶
B．端粒酶
C．末端转移酶
D．甲基转移酶
E．连接酶

答案

参考答案：A

解析：反转录酶先合成一条与RNA模板互补的DNA单链。

单项选择题

Object-oriented analysis (OOA) is a semiformal specification technique for the object-oriented paradigm. Object-oriented analysis consists of three steps. The first step is (71) . It determines how the various results are computed by the product and presents this information in the form of a (72) and associated scenarios. The second is (73) , which determines the classes and their attributes. Then determine the interrelationships and interaction among the classes. The last step is (74) , which determines the actions performed by or to each class or subclass and presents this information in the form of (75) .

（75）处填（）。

A．activity diagram

B．component diagram

C．sequence diagram

D．state diagram
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选择题

不能实现下列物质间直接转化的元素是

A．碳

B．氮

C．硫

D．铝
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