异步传输模式技术中“异步”的含义是( )。
A．采用的是异步串行通信技术
B．网络接口采用的是异步控制方式
C．周期性地插入ATM信元
D．随时插入ATM信元
参考答案：C
解析： 宽带综合业务数字网(B-ISDN)的核心技术是采用异步传输模式(ATM)，实现高效的传输、交换和复用，其带宽可以在155 Mbit/s以上，其中“异步”指周期性的插入ATM信元。
选择下列各句，填入短文中的空白处，使短文意思完整。
By 1960, about 70 percent of the world’s people lived in developing countries. Today it is 80 percent, and 95 percent of the world’s population growth is taking place in these countries.(67)____, as have Latin America and the Caribbean area. North America’s population has grown by a half, while Europe’s has risen by only 20 percent and is now stable. (68) ______-- not because of birth, but of the coming of people from the rest of the world. In 8,000 BC, only 5 million people were alive. (69)_____.To meet those needs humans are using lots of things on the earth in a wrong way -- for example, cutting down too many trees and catching too many fish. These wrong doings are dangerous for human life and health around the world. At the beginning of the 21st century, nearly 60 percent of 4.8 billion people in developing countries have no basic sanitation. Almost a third don’t have enough clean water. A quarter don’t have enough housing. (70)_______. |