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问题 单项选择题

某双链DNA分子中含20%的A＋T，那么，由它转录成的RNA中，G＋C应占全部碱基总数的比率为（）。

A.20%

B.40%

C.60%

D.80%

答案

参考答案：D

单项选择题

Networks can be interconnected by different devices. In the physical layer, networks can be connected by （66） or hubs, which just move the bits from one network to an identical network. One layer up we find bridges and switches, which operate at data link layer. They can accept （67） , examine the MAC address, and forward the frames to a different network while doing minor protocol translation in the process. In the network layer, we have routers that can connect two networks. If two networks have （68） network layer, the router may be able to translate between the packet formats. In the transport layer we find transport gateway, which can interface between two transport connections. Finally, in the application layer, application gateways translate message （69） . As an example, gateways between Internet e-mail and X.400 e-mail must （70） the e-mail message and change various header fields.

（71）处填（）。

A．function

B．definition

C．specification

D．statement
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单项选择题

行政领导者的最主要职能是( )。

A．组织指挥职能
B．知人善任职能
C．科学决策职能
D．协调监督职能
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