在下列传输介质中，哪一种错误率最低( )

A．同轴电缆

B．光缆

C．微波

D．双绞线

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet. Communicating via e-mail is by far the most common Intemet activity. You can （）with anyone in the world who has an Intemet address or e-mail （）with a system connection to the Internet. All you need is （）the Internet and an e-mail program. Two of the most widely used e-mail programs are Microsoft’s （） and Netscape’s Navigator. A typical e-mail message has three basic （）: header, message, and signature.

A typical e-mail message has three basic（）: header, message, and signature.

A．packets

B．elements

C．frames

D．cells