Traditional Internet access methods like dial-up were so slow that host computers were connected to the dial-up (1) at the customer premise over slow (2) ports. PPP was designed to run directly over these serial links. But with the advent of broadband Internet (3) technologies such as ADSL and cable modems there has been a considerable increase in the bandwidth delivered to the end users. This means that the host computers at the customer premise connect to the (4) or cable "modem" over a much faster medium such as Ethernet. It also means that multiple (5) can connect to the Internet through the same connection.

（4）应填入（）

A．FDDI

B．HDSL

C．ADSL

D．CDMA

用氢气还原氧化铜制得6.4g铜，请你计算参加反应的氢气的质量．